perf ui/gtk: Add GTK info_bar widget to browser window

The GtkInfoBar is a modern UI component to display messages without
bothering the main window. It'll be used for showing a warning message.

As the GtkInfoBar requires 2.18 (or newer) version of GTK+ library, add
availability check to Makefile too.

Suggested-by: Sunjin Yang <fan4326@gmail.com>
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1338265382-6872-7-git-send-email-namhyung@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/config/feature-tests.mak

@@ -78,6 +78,19 @@ int main(int argc, char *argv[])
         return 0;
 }
 endef
+
+define SOURCE_GTK2_INFOBAR
+#pragma GCC diagnostic ignored \"-Wstrict-prototypes\"
+#include <gtk/gtk.h>
+#pragma GCC diagnostic error \"-Wstrict-prototypes\"
+
+int main(void)
+{
+	gtk_info_bar_new();
+
+	return 0;
+}
+endef
 endif
 
 ifndef NO_LIBPERL