Include <stdio.h> to avoid an implicit declaration of the printf
function.  Otherwise, the check always fails with compilers that
do not support implicit function declarations (a C feature removed
in 1999).

Submitted upstream: <https://github.com/lldpd/lldpd/pull/565>

diff --git a/configure b/configure
index 931bb75d69c1149d..d34641df4b3d8aed 100755
--- a/configure
+++ b/configure
@@ -18675,7 +18675,7 @@ else
 
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
+#include <stdio.h>
 int
 main ()
 {
diff --git a/m4/progname.m4 b/m4/progname.m4
index 28ac1748f7005139..63ddda6ab9003e5d 100644
--- a/m4/progname.m4
+++ b/m4/progname.m4
@@ -3,7 +3,7 @@
 #
 AC_DEFUN([lldp_CHECK___PROGNAME],[
   AC_CACHE_CHECK([whether libc defines __progname], lldp_cv_check___progname, [
-    AC_TRY_LINK([],
+    AC_TRY_LINK([#include <stdio.h>],
 	[ extern char *__progname; printf("%s", __progname); ],
 	[ lldp_cv_check___progname="yes" ],
 	[ lldp_cv_check___progname="no" ])