Fix crash boehmgc-7.2c on Mac OS X 10.8 Mountain Lion

patch-misc.c.diff

--- misc.c.orig	2012-07-31 21:33:45.000000000 +0900
+++ misc.c	2012-07-31 21:34:09.000000000 +0900
@@ -283,7 +283,7 @@
   /* not static because it could also be errorneously defined in .S     */
   /* file, so this error would be caught by the linker.                 */
   /*ARGSUSED*/
-  void * GC_clear_stack_inner(void *arg, ptr_t limit)
+  void * GC_clear_stack_inner(void *arg, volatile ptr_t limit)
   {
     word dummy[CLEAR_SIZE];