efilink: fix build with gcc 4.8

intptr_t is undefined without an include on stdint.h

Fixes:
 - http://autobuild.buildroot.org/results/a0ca37b5ed27af445344e3ac49dc87bb17512c50

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

inc/efilink.h

@@ -1,6 +1,10 @@
 #ifndef _EFI_LINK_H
 #define _EFI_LINK_H
 
+#if defined(__GNUC__)
+#include <stdint.h>
+#endif
+
 /*++
 
 Copyright (c) 1998  Intel Corporation