[Cogl] [PATCH] configure: Fix the check for _Static_assert

[Neil Roberts]

The check for whether the compiler supports _Static_assert didn't work
properly because the AC_TRY_COMPILE function puts the source
definition in its own main function. The test therefore ends up
declaring a nested main function which GCC allows. If _Static_assert
isn't available then it just looks like an implicit declaration of a
function which only causes a warning in GCC so it would still compile.

This patch changes it to use AC_COMPILE_IFELSE instead. This macro
makes it possible to specify the complete source code so
_Static_assert can be called from the global scope. AC_LANG_PROGRAM is
used to generate the program. For extra aesthetics it now also
generates a 'checking for...' message while the script is running.
---
 configure.ac |   17 +++++++----------
 1 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/configure.ac b/configure.ac
index 8984351..88ab27d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -929,16 +929,13 @@ AC_C_CONST
 dnl     ============================================================
 dnl     Compiler features
 dnl     ============================================================
-AC_TRY_COMPILE([],
-[
-_Static_assert (1, "");
-int
-main (int argc, char **argv)
-{
-  return 0;
-}
-],
-[AC_DEFINE([HAVE_STATIC_ASSERT], [1], [Whether _Static_assert can be used or not])])
+AC_MSG_CHECKING([for _Static_assert])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([_Static_assert (1, "");],
+                                   [(void) 0])],
+                  [AC_DEFINE([HAVE_STATIC_ASSERT], [1],
+                             [Whether _Static_assert can be used or not])
+                   AC_MSG_RESULT([yes])],
+                  [AC_MSG_RESULT([no])])
 
 dnl ================================================================
 dnl Libtool stuff.
-- 
1.7.3.16.g9464b