Update configure for building in strict C99 mode

Related to:

  <https://fedoraproject.org/wiki/Changes/PortingToModernC>
  <https://fedoraproject.org/wiki/Toolchain/PortingToModernC>

tcl-configure-c99.patch

@@ -0,0 +1,28 @@
+Avoid calling the exit function without declaring it first.
+
+Submitted upstream here:
+
+https://core.tcl-lang.org/tcl/tktview/d550f4837a078ff3054d3b00a156d8a11fb628cf
+
+diff --git a/unix/tcl.m4 b/unix/tcl.m4
+index ed12cda75bbc4ad9..d77184421bf8df16 100644
+--- a/unix/tcl.m4
++++ b/unix/tcl.m4
+@@ -2352,7 +2352,7 @@ AC_DEFUN([SC_TIME_HANDLER], [
+ 	AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <time.h>]],
+ 	[[extern long timezone;
+ 	    timezone += 1;
+-	    exit (0);]])],
++	    return 0;]])],
+ 	    [tcl_cv_timezone_long=yes], [tcl_cv_timezone_long=no])])
+     if test $tcl_cv_timezone_long = yes ; then
+ 	AC_DEFINE(HAVE_TIMEZONE_VAR, 1, [Should we use the global timezone variable?])
+@@ -2364,7 +2364,7 @@ AC_DEFUN([SC_TIME_HANDLER], [
+ 	    AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <time.h>]],
+ 	    [[extern time_t timezone;
+ 		timezone += 1;
+-		exit (0);]])],
++		return 0;]])],
+ 		[tcl_cv_timezone_time=yes], [tcl_cv_timezone_time=no])])
+ 	if test $tcl_cv_timezone_time = yes ; then
+ 	    AC_DEFINE(HAVE_TIMEZONE_VAR, 1, [Should we use the global timezone variable?])

tcl.spec

@@ -21,6 +21,7 @@ Patch0: tcl-8.6.12-autopath.patch
 Patch1: tcl-8.6.12-conf.patch
 Patch2: tcl-8.6.12-hidden.patch
 Patch3: tcl-8.6.10-tcltests-path-fix.patch
+Patch4: tcl-configure-c99.patch
 
 %if %sdt
 BuildRequires: systemtap-sdt-devel
@@ -67,6 +68,7 @@ chmod -x generic/tclStrToD.c
 %patch1 -p1 -b .conf
 %patch2 -p1 -b .hidden
 %patch3 -p1 -b .tcltests-path-fix
+%patch4 -p1 -b .configure-c99
 
 %build
 pushd unix