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 <[e-mail]>
Acked-by: Palmer Dabbelt <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]/
Cc: [e-mail]
Signed-off-by: Kees Cook <[e-mail]>

scripts/gcc-plugins/gcc-common.h

···
 #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"
···
 #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"