gcc-plugins: Add support for passing plugin arguments

The latent_entropy plugin needs to pass arguments, so this adds the
support.

Signed-off-by: Emese Revfy <re.emese@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

scripts/Makefile.gcc-plugins

@@ -19,7 +19,7 @@ ifdef CONFIG_GCC_PLUGINS
     endif
   endif
 
-  GCC_PLUGINS_CFLAGS := $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y))
+  GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y))
 
   export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN SANCOV_PLUGIN