gcc-plugins: remove support for GCC 4.9 and older

The minimum GCC version has been bumped to 5.1, so we can get rid of all
the compatibility code for anything older than that.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210922182632.633394-1-ardb@kernel.org

scripts/gcc-plugins/structleak_plugin.c

@@ -103,10 +103,8 @@ static void finish_type(void *event_data, void *data)
 	if (type == NULL_TREE || type == error_mark_node)
 		return;
 
-#if BUILDING_GCC_VERSION >= 5000
 	if (TREE_CODE(type) == ENUMERAL_TYPE)
 		return;
-#endif
 
 	if (TYPE_USERSPACE(type))
 		return;