gcc-plugins: randstruct: Update code comment in relayout_struct()

Update code comment to clarify that the only element whose layout is
not randomized is a proper C99 flexible-array member. This update is
complementary to commit 1ee6035 ("gcc-plugins: randstruct: Only
warn about true flexible arrays")

Signed-off-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/ZWJr2MWDjXLHE8ap@work
Fixes: 1ee6035 ("gcc-plugins: randstruct: Only warn about true flexible arrays")
Signed-off-by: Kees Cook <keescook@chromium.org>

Author: GustavoARSilva

scripts/gcc-plugins/randomize_layout_plugin.c

@@ -339,8 +339,7 @@ static int relayout_struct(tree type)
 
 	/*
 	 * enforce that we don't randomize the layout of the last
-	 * element of a struct if it's a 0 or 1-length array
-	 * or a proper flexible array
+	 * element of a struct if it's a proper flexible array
 	 */
 	if (is_flexible_array(newtree[num_fields - 1])) {
 		has_flexarray = true;