util/grub-module-verifierXX: Enable running standalone checkers

Allow treating util/grub-module-verifierXX.c as a file you can build
directly so syntax checkers like vim's "syntastic" plugin, which uses
"gcc -x c -fsyntax-only" to build it, will work.

One still has to do whatever setup is required to make it pick the
right include dirs, which -I options we use, etc., but this makes
it so you can do the checking on the file you're editing, rather
than on a different file.

Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Robbie Harwood <rharwood@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

util/grub-module-verifier64.c

@@ -1,2 +1,4 @@
 #define MODULEVERIFIER_ELF64 1
+#ifndef GRUB_MODULE_VERIFIERXX
 #include "grub-module-verifierXX.c"
+#endif