src: avoid creating local data variable

This commit removes the following comment and attempts to fix the issue
as the the requirement of g++ version is now 4.9.4 or newer:

// XXX(bnoordhuis) Work around a g++ 4.9.2 template type inferrer bug
// when the expression is written as info.Data().As<v8::External>().

PR-URL: #14732
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

src/env-inl.h

@@ -283,10 +283,8 @@ template <typename T>
 inline Environment* Environment::GetCurrent(
     const v8::PropertyCallbackInfo<T>& info) {
   CHECK(info.Data()->IsExternal());
-  // XXX(bnoordhuis) Work around a g++ 4.9.2 template type inferrer bug
-  // when the expression is written as info.Data().As<v8::External>().
-  v8::Local<v8::Value> data = info.Data();
-  return static_cast<Environment*>(data.As<v8::External>()->Value());
+  return static_cast<Environment*>(
+      info.Data().template As<v8::External>()->Value());
 }
 
 inline Environment::Environment(IsolateData* isolate_data,