vm_backtrace.c: suppress warning

* vm_backtrace.c (rb_debug_inspector_open): suppress
  uninitialized-variable warning.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38049 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

vm_backtrace.c

@@ -938,7 +938,7 @@ rb_debug_inspector_open(rb_debug_inspector_func_t func, void *data)
     rb_debug_inspector_t dbg_context;
     rb_thread_t *th = GET_THREAD();
     int state;
-    VALUE result;
+    volatile VALUE UNINITIALIZED_VAR(result);
 
     dbg_context.th = th;
     dbg_context.cfp = dbg_context.th->cfp;