meson,configure: include config.h automatically

This will prevent any more missing `#include "config.h"` bug, at the
cost of having to recompile some files that didn't need to be when
changing build options.

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
diff --git a/configure.ac b/configure.ac
index 0e36336..619af49 100644
--- a/configure.ac
+++ b/configure.ac
@@ -541,6 +541,8 @@
     AC_DEFINE(HAVE_VISIBILITY, 0)
 fi
 
+CFLAGS="$CFLAGS -include config.h"
+
 AC_SUBST(WARN_CFLAGS)
 AC_CONFIG_FILES([
 	Makefile