gcc-plugins: Reorganize gimple includes for GCC 13

The gimple-iterator.h header must be included before gimple-fold.h
starting with GCC 13. Reorganize gimple headers to work for all GCC
versions.

Reported-by: Palmer Dabbelt <palmer@rivosinc.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Link: https://lore.kernel.org/all/20230113173033.4380-1-palmer@rivosinc.com/
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

Author: kees

scripts/gcc-plugins/gcc-common.h

@@ -71,7 +71,9 @@
 #include "varasm.h"
 #include "stor-layout.h"
 #include "internal-fn.h"
+#include "gimple.h"
 #include "gimple-expr.h"
+#include "gimple-iterator.h"
 #include "gimple-fold.h"
 #include "context.h"
 #include "tree-ssa-alias.h"
@@ -85,10 +87,8 @@
 #include "tree-eh.h"
 #include "stmt.h"
 #include "gimplify.h"
-#include "gimple.h"
 #include "tree-phinodes.h"
 #include "tree-cfg.h"
-#include "gimple-iterator.h"
 #include "gimple-ssa.h"
 #include "ssa-iterators.h"