MAINTAINERS: add GCC plugins Makefile

Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

MAINTAINERS

@@ -5196,6 +5196,7 @@ L:	kernel-hardening@lists.openwall.com
 S:	Maintained
 F:	scripts/gcc-plugins/
 F:	scripts/gcc-plugin.sh
+F:	scripts/Makefile.gcc-plugins
 F:	Documentation/gcc-plugins.txt
 
 GCOV BASED KERNEL PROFILING