gcc-plugins/structleak: add makefile var for disabling structleak

KUnit and structleak don't play nice, so add a makefile variable for
enabling structleak when it complains.
Co-developed-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NBrendan Higgins <brendanhiggins@google.com>
Reviewed-by: NDavid Gow <davidgow@google.com>
Signed-off-by: NShuah Khan <skhan@linuxfoundation.org>

scripts/Makefile.gcc-plugins

@@ -19,6 +19,10 @@ gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF)		\
 		+= -fplugin-arg-structleak_plugin-byref
 gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL)	\
 		+= -fplugin-arg-structleak_plugin-byref-all
+ifdef CONFIG_GCC_PLUGIN_STRUCTLEAK
+    DISABLE_STRUCTLEAK_PLUGIN += -fplugin-arg-structleak_plugin-disable
+endif
+export DISABLE_STRUCTLEAK_PLUGIN
 gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK)		\
 		+= -DSTRUCTLEAK_PLUGIN