Define _GNU_SOURCE in the math tests so that exp10 can be found.
Include <stdio.h> for the puts function in the __progname check.

Submitted upstream: <https://gitlab.com/gambas/gambas/-/merge_requests/286>

diff --git a/acinclude.m4 b/acinclude.m4
index 055cfd86b1102815..fe4f24b9f49cd1d7 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -558,6 +558,7 @@ AC_DEFUN([GB_CHECK_MATH_FUNC],
     [
       #define _ISOC9X_SOURCE	1
       #define _ISOC99_SOURCE	1
+      #define _GNU_SOURCE	1
       #define __USE_ISOC99	1
       #define __USE_ISOC9X	1
       #include <math.h>
diff --git a/gb.httpd/configure.ac b/gb.httpd/configure.ac
index 5fb0fa507ff89993..e8a3a9e3a4dfe8fb 100644
--- a/gb.httpd/configure.ac
+++ b/gb.httpd/configure.ac
@@ -28,7 +28,7 @@ dnl
 AC_MSG_CHECKING(how to link static binaries)
 AC_CACHE_VAL(ac_cv_lbl_static_flag,
     ac_cv_lbl_static_flag=unknown
-    echo 'main() {}' > conftest.c
+    echo 'int main() {}' > conftest.c
     if test "$GCC" != yes ; then
 	    trial_flag="-Bstatic"
 	    test=`$CC $trial_flag -o conftest conftest.c 2>&1`
@@ -53,7 +53,7 @@ fi
 
 AC_MSG_CHECKING(for __progname)
 AC_CACHE_VAL(ac_cv_extern__progname,
-    AC_TRY_LINK([],
+    AC_TRY_LINK([#include <stdio.h>],
 	[extern char *__progname; 
 	puts(__progname)],
 	ac_cv_extern__progname=yes,