Performance-killing bug workaround for V8 on mingw

When V8 on mingw generates a _compiled_ call stub for an external api callback, it fucks up the stack.
It doesn't set the stack pointers properly. Could be due to subtly different calling conventions?
This patch disables the simple_api_call optimization. It hurts performance.

deps/v8/src/stub-cache.h

@@ -762,6 +762,11 @@ class CallOptimization BASE_EMBEDDED {
   }
 
   bool is_simple_api_call() const {
+    // As of V8 2.6.8 simple api call optimization causes segfaults on MINGW
+    // Disable it until this gets resolved
+#ifdef __MINGW32__
+    return false;
+#endif
     return is_simple_api_call_;
   }