Prevent MJIT compilation from running while moving

pointers.

Instead of 4fe908c, just locking the MJIT
worker may be fine for this case. And also we might have the same issue
in all `gc_compact_after_gc` calls.

gc.c

@@ -8272,6 +8272,8 @@ gc_compact_after_gc(rb_objspace_t *objspace, int use_toward_empty, int use_doubl
 {
     if (0) fprintf(stderr, "gc_compact_after_gc: %d,%d,%d\n", use_toward_empty, use_double_pages, use_verifier);
 
+    mjit_gc_start_hook(); // prevent MJIT from running while moving pointers related to ISeq
+
     if (use_verifier) {
         gc_verify_internal_consistency(Qnil);
     }
@@ -8315,6 +8317,8 @@ gc_compact_after_gc(rb_objspace_t *objspace, int use_toward_empty, int use_doubl
     (void)moved_list;
 #endif
 
+    mjit_gc_exit_hook(); // unlock MJIT here, because `rb_gc()` calls `mjit_gc_start_hook()` again.
+
     /* GC after compaction to eliminate T_MOVED */
     rb_gc();
 }