Disable peephole optimizer on mips64 and sparc64, since it occasionally
segfaults.

Index: compile.c
--- compile.c.orig
+++ compile.c
@@ -2877,6 +2877,10 @@ static int
 iseq_peephole_optimize(rb_iseq_t *iseq, LINK_ELEMENT *list, const int do_tailcallopt)
 {
     INSN *const iobj = (INSN *)list;
+#if defined(__mips64__) || defined(__sparc64__)
+    return COMPILE_OK;
+#endif
+
 
   again:
     optimize_checktype(iseq, iobj);