--- a/configure.ac	2016-09-11 17:47:25.000000000 +0100
+++ b/configure.ac	2016-09-16 18:06:48.931414048 +0100
@@ -154,7 +154,8 @@
   [], [AC_MSG_ERROR([Missing/unusable system header file <$ac_header>])])
 
 # check for kernel headers
-CPPFLAGS="$kernelinc"
+SAV_CPPFLAGS="$CPPFLAGS"
+CPPFLAGS="$CPPFLAGS $kernelinc"
 dnl -- <linux/netlink.h> needed <sys/socket.h> until Linux 3.1
 dnl -- using AC_CHECK_HEADER causes a horrible error message for the user
 NETLINK_EXTRA_INCLUDE=
@@ -176,6 +177,7 @@
 AC_CHECK_HEADERS([linux/if_arp.h],
   [], [AC_MSG_ERROR([Missing/unusable <$ac_header>])],
   [[#include <sys/socket.h>]])
+CPPFLAGS="$SAV_CPPFLAGS"
 
 # Checks for typedefs, structures, and compiler characteristics.
 AC_HEADER_STDBOOL
@@ -303,16 +305,19 @@
   ])
 
 if test $NETLINK_VER != None; then
-  CPPFLAGS="$kernelinc"
+  SAV_CPPFLAGS="$CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $kernelinc"
   AC_CHECK_HEADERS(libnfnetlink/libnfnetlink.h,,AC_MSG_ERROR([
     !!! Please install libnfnetlink headers.              !!!]))
   if test $NETLINK_VER = 3; then
-    CPPFLAGS="$NL3_CFLAGS"
+    CPPFLAGS="$CPPFLAGS $NL3_CFLAGS"
     AC_CHECK_HEADERS([netlink/route/link.h netlink/route/link/inet.h], [], [AC_MSG_ERROR([libnl-3 headers missing])])
   fi
 
   AC_CHECK_HEADERS([linux/rtnetlink.h], [], [AC_MSG_ERROR([Unusable link/rtnetlink.h])], [$NETLINK_EXTRA_INCLUDE])
   AC_CHECK_HEADERS([libnfnetlink/libnfnetlink.h netlink/genl/ctrl.h netlink/genl/genl.h netlink/netlink.h], [], [AC_MSG_ERROR([netlink headers missing])])
+
+  CPPFLAGS="$SAV_CPPFLAGS"
 fi
 
 dnl -- Check for the following variables introduced at various times into Linux
@@ -347,7 +352,8 @@
 dnl -- Resolved in libnl3-3.2.26 (release 30/3/2015)
 if test $NETLINK_VER = 3; then
   AC_MSG_CHECKING([for net/if.h and libnl3/netlink/route/link.h namespace collision])
-  CPPFLAGS="$NL3_CFLAGS"
+  SAV_CPPFLAGS="$CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $NL3_CFLAGS"
   AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
       #include <net/if.h>
       #include <netlink/route/link.h>
@@ -358,12 +364,14 @@
       AC_DEFINE([_HAVE_IF_H_LINK_H_COLLISION_], [ 1 ], [Define to 1 if <net/if.h> and <netlink/route/link.h> namespace collision])
       add_build_opt([IF_H_LINK_H_COLLISION])
     ])
+  CPPFLAGS="$SAV_CPPFLAGS"
 fi
 
 dnl ----[Check have IPV4_DEVCONF defines - since Linux 3.11]----
 if test $NETLINK_VER = 3; then
   IPV4_DEVCONF=Yes
-  CPPFLAGS="$kernelinc"
+  SAV_CPPFLAGS="$CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $kernelinc"
   AC_CHECK_DECLS([
     IPV4_DEVCONF_ARP_IGNORE,
     IPV4_DEVCONF_ACCEPT_LOCAL,
@@ -375,6 +383,7 @@
       break
     ],
     [[#include <linux/ip.h>]])
+  CPPFLAGS="$SAV_CPPFLAGS"
 else
   IPV4_DEVCONF=No
 fi
@@ -397,20 +406,23 @@
   if test $USE_LIBIPTC = Yes; then
     add_pkg_config([--static libiptc], [IPTC])
     LIBS="$IPTC_LIBS"
-    CPPFLAGS="$kernelinc"
+    SAV_CPPFLAGS="$CPPFLAGS"
+    CPPFLAGS="$CPPFLAGS $kernelinc"
     AC_CHECK_LIB(iptc, iptc_init,
       [
         add_pkg_config([--static libiptc])
         AC_DEFINE([_HAVE_LIBIPTC_], [ 1 ], [Define to 1 if have iptables libraries])
       ],
       [USE_LIBIPTC=No])
+  CPPFLAGS="$SAV_CPPFLAGS"
   fi
 
   if test $USE_LIBIPTC = Yes; then
     add_build_opt([LIBIPTC])
 
     dnl ----[Check for ipset libraries]----
-    CPPFLAGS="$kernelinc"
+    SAV_CPPFLAGS="$CPPFLAGS"
+    CPPFLAGS="$CPPFLAGS $kernelinc"
     if test "${enable_libipset}" != no; then
       pkg-config --exists libipset
       if test $? -eq 0; then
@@ -478,6 +490,8 @@
     AC_CHECK_DECL([XT_EXTENSION_MAXNAMELEN], [],
       [AC_DEFINE([XT_EXTENSION_MAXNAMELEN], [ (XT_FUNCTION_MAXNAMELEN - 1) ], [Define if <linux/netfilter/x_tables.h> doesnt define it])],
       [#include <linux/netfilter/x_tables.h>])
+
+    CPPFLAGS="$SAV_CPPFLAGS"
   fi
 fi
 AM_CONDITIONAL([LIBIPTC], [test $USE_LIBIPTC = Yes])
@@ -488,7 +502,8 @@
 # Linux 4.5 to 4.5.4 has <libiptc/libiptc.h> indirectly including <net/if.h>
 # and <linux/if.h> which causes a namespace collision.
 AC_MSG_CHECKING([for libiptc/libiptc.h linux/if.h and net/if.h namespace collision])
-CPPFLAGS="$kernelinc"
+SAV_CPPFLAGS="$CPPFLAGS"
+CPPFLAGS="$CPPFLAGS $kernelinc"
 AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
     #include <libiptc/libiptc.h>
   ]])],
@@ -500,6 +515,7 @@
     AC_DEFINE([_HAVE_LINUX_NET_IF_H_COLLISION_], [ 1 ], [Define to 1 if have libiptc/libiptc.h linux/if.h and net/if.h namespace collision])
     add_build_opt([LINUX_NET_IF_H_COLLISION])
   ])
+CPPFLAGS="$SAV_CPPFLAGS"
 
 dnl ----[ Checks for LVS and VRRP support ]----
 IPVS_SYNCD_ATTRIBUTES=No
@@ -518,7 +534,8 @@
   fi
 
   dnl ----[ IPVS syncd options ]---
-  CPPFLAGS="$kernelinc"
+  SAV_CPPFLAGS="$CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $kernelinc"
   IPVS_SYNCD_ATTRIBUTES=Yes
   AC_CHECK_DECLS([
     IPVS_DAEMON_ATTR_SYNC_MAXLEN,
@@ -540,7 +557,6 @@
   dnl ----[ IPVS 64-bit stats ]----
   dnl -- Since Linux 4.2
   if test "$enable_lvs_64bit_stats" != "no"; then
-    CPPFLAGS="$kernelinc"
     IPVS_64BIT_STATS=Yes
     AC_CHECK_DECLS([
       IPVS_SVC_ATTR_STATS64,
@@ -555,6 +571,7 @@
       add_build_opt([IPVS_64BIT_STATS])
     fi
   fi
+  CPPFLAGS="$SAV_CPPFLAGS"
 else
   IPVS_SUPPORT=No
 fi
@@ -577,7 +594,8 @@
   fi
 
   dnl ----[ Checks for kernel VMAC support ]----
-  CPPFLAGS="$kernelinc"
+  SAV_CPPFLAGS="$CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $kernelinc"
   MACVLAN_SUPPORT=Yes
   dnl -- Since Linux 2.6.33
   AC_CHECK_DECLS([
@@ -594,6 +612,7 @@
     AC_DEFINE([_HAVE_VRRP_VMAC_], [ 1 ], [Define to 1 if have MAC VLAN support])
     add_build_opt([VRRP_VMAC])
   fi
+  CPPFLAGS="$SAV_CPPFLAGS"
 fi
 AM_CONDITIONAL([WITH_VRRP], [test $VRRP_SUPPORT = Yes])
 AM_CONDITIONAL([VRRP_AUTH], [test $VRRP_AUTH_SUPPORT = Yes])
@@ -614,7 +633,8 @@
 
 dnl ----[ Checks for FIB routing support ]----
 # Introduced in Linux 2.6.19
-CPPFLAGS="$kernelinc"
+SAV_CPPFLAGS="$CPPFLAGS"
+CPPFLAGS="$CPPFLAGS $kernelinc"
 AC_CHECK_DECL([FRA_SRC],
   [
     FIB_ROUTING_SUPPORT=Yes
@@ -626,9 +646,11 @@
   ],[[#include <sys/socket.h>
       #include <linux/fib_rules.h>]])
 AM_CONDITIONAL([FIB_ROUTING], [test $FIB_ROUTING_SUPPORT = Yes])
+CPPFLAGS="$SAV_CPPFLAGS"
 
 dnl ----[ Checks for kernel IFLA_INET6_ADDR_GEN_MODE support ]----
-CPPFLAGS="$kernelinc"
+SAV_CPPFLAGS="$CPPFLAGS"
+CPPFLAGS="$CPPFLAGS $kernelinc"
 if test ${MACVLAN_SUPPORT} = Yes; then
   # Introduced in Linux 3.17
   AC_CHECK_DECLS([IFLA_INET6_ADDR_GEN_MODE],
@@ -638,6 +660,7 @@
       #include <linux/if_link.h>
     ]])
 fi
+CPPFLAGS="$SAV_CPPFLAGS"
 
 dnl ----[ Checks for SNMP support ]----
 SNMP_SUPPORT=No
@@ -662,8 +685,10 @@
   NETSNMP_LIBS="$NETSNMP_LIBS_AGENT $NETSNMP_LIBS_EXT"
   NETSNMP_CFLAGS="`${NETSNMP_CONFIG} --base-cflags` -DNETSNMP_NO_INLINE"
 
-  CFLAGS="${NETSNMP_CFLAGS}"
-  LIBS="${NETSNMP_LIBS}"
+  SAV_CFLAGS="$CFLAGS"
+  CFLAGS="$CFLAGS ${NETSNMP_CFLAGS}"
+  SAV_LIBS="$LIBS"
+  LIBS="$LIBS ${NETSNMP_LIBS}"
   AC_MSG_CHECKING([whether C compiler supports flag "${NETSNMP_CFLAGS} ${NETSNMP_LIBS}" from Net-SNMP])
   AC_LINK_IFELSE([AC_LANG_SOURCE([[
       int main(void)
@@ -683,7 +708,8 @@
 
   # check for net-snmp headers
   # Some ancient distributions may miss <net-snmp/agent/util_funcs.h> header
-  CPPFLAGS="$NETSNMP_CFLAGS"
+  SAV_CPPFLAGS="$CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $NETSNMP_CFLAGS"
   AC_CHECK_HEADERS(net-snmp/agent/agent_sysORTable.h net-snmp/agent/snmp_vars.h net-snmp/agent/util_funcs.h,[],
     [AC_MSG_ERROR([missing net-snmp headers])],[[
       #include <net-snmp/net-snmp-config.h>
@@ -739,8 +765,9 @@
     AC_MSG_ERROR([CHECKER SNMP support requires checker])
   fi
 
-  unset LIBS
-  unset CFLAGS
+  CPPFLAGS="$SAV_CPPFLAGS"
+  CFLAGS="$SAV_CFLAGS"
+  LIBS="$SAV_LIBS"
 fi
 
 dnl ----[What SNMP support is required]----
@@ -798,10 +825,12 @@
 
 dnl ---[ check for setns() ]----
 dnl -- CLONE_NEWNET defined from Linux 3.0
-CFLAGS=-D_GNU_SOURCE
+SAV_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -D_GNU_SOURCE"
 AC_CHECK_DECLS([CLONE_NEWNET], [], [], [[#include <sched.h>]])
 dnl -- From glibc 2.14. Otherwise use setns syscall, since Linux 2.4.x
 AC_CHECK_FUNCS([setns])
+CFLAGS="$SAV_CFLAGS"
 AM_CONDITIONAL([WITH_NAMESPACES], [test $ac_cv_have_decl_CLONE_NEWNET = yes])
 
 dnl ---[ check for sphinx-build executable ]----
--- a/configure	2016-09-11 18:17:50.000000000 +0100
+++ b/configure	2016-09-16 18:06:48.934413991 +0100
@@ -2527,7 +2527,7 @@
 ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
-am__api_version='1.14'
+am__api_version='1.15'
 
 ac_aux_dir=
 for ac_dir in "$srcdir" "$srcdir/.." "$srcdir/../.."; do
@@ -2728,8 +2728,8 @@
 ac_script='s/[\\$]/&&/g;s/;s,x,x,$//'
 program_transform_name=`$as_echo "$program_transform_name" | sed "$ac_script"`
 
-# expand $ac_aux_dir to an absolute path
-am_aux_dir=`cd $ac_aux_dir && pwd`
+# Expand $ac_aux_dir to an absolute path.
+am_aux_dir=`cd "$ac_aux_dir" && pwd`
 
 if test x"${MISSING+set}" != xset; then
   case $am_aux_dir in
@@ -2748,7 +2748,7 @@
 $as_echo "$as_me: WARNING: 'missing' script is too old or missing" >&2;}
 fi
 
-if test x"${install_sh}" != xset; then
+if test x"${install_sh+set}" != xset; then
   case $am_aux_dir in
   *\ * | *\	*)
     install_sh="\${SHELL} '$am_aux_dir/install-sh'" ;;
@@ -3076,8 +3076,8 @@
 # <http://lists.gnu.org/archive/html/automake/2012-07/msg00014.html>
 mkdir_p='$(MKDIR_P)'
 
-# We need awk for the "check" target.  The system "awk" is bad on
-# some platforms.
+# We need awk for the "check" target (and possibly the TAP driver).  The
+# system "awk" is bad on some platforms.
 # Always define AMTAR for backward compatibility.  Yes, it's still used
 # in the wild :-(  We should find a proper way to deprecate it ...
 AMTAR='$${TAR-tar}'
@@ -3137,6 +3137,7 @@
 
 
 
+
 ac_config_headers="$ac_config_headers lib/config.h"
 
 
@@ -5259,7 +5260,8 @@
 
 
 # check for kernel headers
-CPPFLAGS="$kernelinc"
+SAV_CPPFLAGS="$CPPFLAGS"
+CPPFLAGS="$CPPFLAGS $kernelinc"
 NETLINK_EXTRA_INCLUDE=
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
@@ -5333,6 +5335,7 @@
 
 done
 
+CPPFLAGS="$SAV_CPPFLAGS"
 
 # Checks for typedefs, structures, and compiler characteristics.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for stdbool.h that conforms to C99" >&5
@@ -6521,7 +6524,8 @@
 
 
 if test $NETLINK_VER != None; then
-  CPPFLAGS="$kernelinc"
+  SAV_CPPFLAGS="$CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $kernelinc"
   for ac_header in libnfnetlink/libnfnetlink.h
 do :
   ac_fn_c_check_header_mongrel "$LINENO" "libnfnetlink/libnfnetlink.h" "ac_cv_header_libnfnetlink_libnfnetlink_h" "$ac_includes_default"
@@ -6538,7 +6542,7 @@
 done
 
   if test $NETLINK_VER = 3; then
-    CPPFLAGS="$NL3_CFLAGS"
+    CPPFLAGS="$CPPFLAGS $NL3_CFLAGS"
     for ac_header in netlink/route/link.h netlink/route/link/inet.h
 do :
   as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
@@ -6586,6 +6590,8 @@
 
 done
 
+
+  CPPFLAGS="$SAV_CPPFLAGS"
 fi
 
 ac_fn_c_check_decl "$LINENO" "RTA_ENCAP" "ac_cv_have_decl_RTA_ENCAP" "#include <linux/rtnetlink.h>
@@ -6743,7 +6749,8 @@
 if test $NETLINK_VER = 3; then
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for net/if.h and libnl3/netlink/route/link.h namespace collision" >&5
 $as_echo_n "checking for net/if.h and libnl3/netlink/route/link.h namespace collision... " >&6; }
-  CPPFLAGS="$NL3_CFLAGS"
+  SAV_CPPFLAGS="$CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $NL3_CFLAGS"
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -6767,11 +6774,13 @@
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+  CPPFLAGS="$SAV_CPPFLAGS"
 fi
 
 if test $NETLINK_VER = 3; then
   IPV4_DEVCONF=Yes
-  CPPFLAGS="$kernelinc"
+  SAV_CPPFLAGS="$CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $kernelinc"
   ac_fn_c_check_decl "$LINENO" "IPV4_DEVCONF_ARP_IGNORE" "ac_cv_have_decl_IPV4_DEVCONF_ARP_IGNORE" "#include <linux/ip.h>
 "
 if test "x$ac_cv_have_decl_IPV4_DEVCONF_ARP_IGNORE" = xyes; then :
@@ -6849,6 +6858,7 @@
 
 fi
 
+  CPPFLAGS="$SAV_CPPFLAGS"
 else
   IPV4_DEVCONF=No
 fi
@@ -6919,7 +6929,8 @@
 
 
     LIBS="$IPTC_LIBS"
-    CPPFLAGS="$kernelinc"
+    SAV_CPPFLAGS="$CPPFLAGS"
+    CPPFLAGS="$CPPFLAGS $kernelinc"
     { $as_echo "$as_me:${as_lineno-$LINENO}: checking for iptc_init in -liptc" >&5
 $as_echo_n "checking for iptc_init in -liptc... " >&6; }
 if ${ac_cv_lib_iptc_iptc_init+:} false; then :
@@ -7002,12 +7013,14 @@
   USE_LIBIPTC=No
 fi
 
+  CPPFLAGS="$SAV_CPPFLAGS"
   fi
 
   if test $USE_LIBIPTC = Yes; then
     BUILD_OPTIONS="$BUILD_OPTIONS LIBIPTC"
 
-        CPPFLAGS="$kernelinc"
+        SAV_CPPFLAGS="$CPPFLAGS"
+    CPPFLAGS="$CPPFLAGS $kernelinc"
     if test "${enable_libipset}" != no; then
       pkg-config --exists libipset
       if test $? -eq 0; then
@@ -7326,6 +7339,8 @@
 
 fi
 
+
+    CPPFLAGS="$SAV_CPPFLAGS"
   fi
 fi
  if test $USE_LIBIPTC = Yes; then
@@ -7350,7 +7365,8 @@
 # and <linux/if.h> which causes a namespace collision.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for libiptc/libiptc.h linux/if.h and net/if.h namespace collision" >&5
 $as_echo_n "checking for libiptc/libiptc.h linux/if.h and net/if.h namespace collision... " >&6; }
-CPPFLAGS="$kernelinc"
+SAV_CPPFLAGS="$CPPFLAGS"
+CPPFLAGS="$CPPFLAGS $kernelinc"
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -7373,6 +7389,7 @@
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+CPPFLAGS="$SAV_CPPFLAGS"
 
 IPVS_SYNCD_ATTRIBUTES=No
 IPVS_64BIT_STATS=No
@@ -7403,7 +7420,8 @@
     BUILD_OPTIONS="$BUILD_OPTIONS LIBIPVS_NETLINK"
   fi
 
-    CPPFLAGS="$kernelinc"
+    SAV_CPPFLAGS="$CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $kernelinc"
   IPVS_SYNCD_ATTRIBUTES=Yes
   ac_fn_c_check_decl "$LINENO" "IPVS_DAEMON_ATTR_SYNC_MAXLEN" "ac_cv_have_decl_IPVS_DAEMON_ATTR_SYNC_MAXLEN" "#include <linux/ip_vs.h>
 "
@@ -7509,7 +7527,6 @@
   fi
 
       if test "$enable_lvs_64bit_stats" != "no"; then
-    CPPFLAGS="$kernelinc"
     IPVS_64BIT_STATS=Yes
     ac_fn_c_check_decl "$LINENO" "IPVS_SVC_ATTR_STATS64" "ac_cv_have_decl_IPVS_SVC_ATTR_STATS64" "#include <linux/ip_vs.h>
 "
@@ -7557,6 +7574,7 @@
       BUILD_OPTIONS="$BUILD_OPTIONS IPVS_64BIT_STATS"
     fi
   fi
+  CPPFLAGS="$SAV_CPPFLAGS"
 else
   IPVS_SUPPORT=No
 fi
@@ -7587,7 +7605,8 @@
     BUILD_OPTIONS="$BUILD_OPTIONS VRRP_AUTH"
   fi
 
-    CPPFLAGS="$kernelinc"
+    SAV_CPPFLAGS="$CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $kernelinc"
   MACVLAN_SUPPORT=Yes
     ac_fn_c_check_decl "$LINENO" "IFLA_MACVLAN_MODE" "ac_cv_have_decl_IFLA_MACVLAN_MODE" "
       #include <sys/socket.h>
@@ -7640,6 +7659,7 @@
 
     BUILD_OPTIONS="$BUILD_OPTIONS VRRP_VMAC"
   fi
+  CPPFLAGS="$SAV_CPPFLAGS"
 fi
  if test $VRRP_SUPPORT = Yes; then
   WITH_VRRP_TRUE=
@@ -7713,7 +7733,8 @@
 
 
 # Introduced in Linux 2.6.19
-CPPFLAGS="$kernelinc"
+SAV_CPPFLAGS="$CPPFLAGS"
+CPPFLAGS="$CPPFLAGS $kernelinc"
 ac_fn_c_check_decl "$LINENO" "FRA_SRC" "ac_cv_have_decl_FRA_SRC" "#include <sys/socket.h>
       #include <linux/fib_rules.h>
 "
@@ -7739,8 +7760,10 @@
   FIB_ROUTING_FALSE=
 fi
 
+CPPFLAGS="$SAV_CPPFLAGS"
 
-CPPFLAGS="$kernelinc"
+SAV_CPPFLAGS="$CPPFLAGS"
+CPPFLAGS="$CPPFLAGS $kernelinc"
 if test ${MACVLAN_SUPPORT} = Yes; then
   # Introduced in Linux 3.17
   ac_fn_c_check_decl "$LINENO" "IFLA_INET6_ADDR_GEN_MODE" "ac_cv_have_decl_IFLA_INET6_ADDR_GEN_MODE" "
@@ -7763,6 +7786,7 @@
 fi
 
 fi
+CPPFLAGS="$SAV_CPPFLAGS"
 
 SNMP_SUPPORT=No
 SNMP_KEEPALIVED_SUPPORT=No
@@ -7883,8 +7907,10 @@
   NETSNMP_LIBS="$NETSNMP_LIBS_AGENT $NETSNMP_LIBS_EXT"
   NETSNMP_CFLAGS="`${NETSNMP_CONFIG} --base-cflags` -DNETSNMP_NO_INLINE"
 
-  CFLAGS="${NETSNMP_CFLAGS}"
-  LIBS="${NETSNMP_LIBS}"
+  SAV_CFLAGS="$CFLAGS"
+  CFLAGS="$CFLAGS ${NETSNMP_CFLAGS}"
+  SAV_LIBS="$LIBS"
+  LIBS="$LIBS ${NETSNMP_LIBS}"
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether C compiler supports flag \"${NETSNMP_CFLAGS} ${NETSNMP_LIBS}\" from Net-SNMP" >&5
 $as_echo_n "checking whether C compiler supports flag \"${NETSNMP_CFLAGS} ${NETSNMP_LIBS}\" from Net-SNMP... " >&6; }
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -7928,7 +7954,8 @@
 
   # check for net-snmp headers
   # Some ancient distributions may miss <net-snmp/agent/util_funcs.h> header
-  CPPFLAGS="$NETSNMP_CFLAGS"
+  SAV_CPPFLAGS="$CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $NETSNMP_CFLAGS"
   for ac_header in net-snmp/agent/agent_sysORTable.h net-snmp/agent/snmp_vars.h net-snmp/agent/util_funcs.h
 do :
   as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
@@ -8000,8 +8027,9 @@
     as_fn_error $? "CHECKER SNMP support requires checker" "$LINENO" 5
   fi
 
-  unset LIBS
-  unset CFLAGS
+  CPPFLAGS="$SAV_CPPFLAGS"
+  CFLAGS="$SAV_CFLAGS"
+  LIBS="$SAV_LIBS"
 fi
 
 if test $SNMP_SUPPORT = Yes; then
@@ -8183,7 +8211,8 @@
 
 fi
 
-CFLAGS=-D_GNU_SOURCE
+SAV_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -D_GNU_SOURCE"
 ac_fn_c_check_decl "$LINENO" "CLONE_NEWNET" "ac_cv_have_decl_CLONE_NEWNET" "#include <sched.h>
 "
 if test "x$ac_cv_have_decl_CLONE_NEWNET" = xyes; then :
@@ -8207,6 +8236,7 @@
 fi
 done
 
+CFLAGS="$SAV_CFLAGS"
  if test $ac_cv_have_decl_CLONE_NEWNET = yes; then
   WITH_NAMESPACES_TRUE=
   WITH_NAMESPACES_FALSE='#'