Narrower scope working around MSC bug

mrbgems/mruby-random/src/random.c

@@ -210,18 +210,18 @@ random_m_srand(mrb_state *mrb, mrb_value self)
  *  Shuffles elements in self in place.
  */
 
-#if defined _MSC_VER && _MSC_VER >= 1900
-#pragma optimize( "", off )
-#endif
 static mrb_value
 mrb_ary_shuffle_bang(mrb_state *mrb, mrb_value ary)
 {
+  mrb_int i;
+  mrb_value max;
  /*
  * MSC compiler generating invalid instructions with optimization
  * enabled
  */
-  mrb_int i;
-  mrb_value max;
+#if defined _MSC_VER && _MSC_VER >= 1923
+  volatile
+#endif
   mrb_value r = mrb_nil_value();
   rand_state *random;