Fixes for Visual Studio 2014

Hello all. Partially fueled by a joke to get PHP to compile on Windows 10, and partially fueled by starting to look more into core, I found some issues with the javascript-based configuration under Windows 10 and Visual Studio 2014 as well as issues where VS2014 includes better C support than older versions of VS. https://github.com/php/php-src/pull/869 The PR adds in some undefined checks for javascript variables, and some version checks for VS2014 to not load as much custom Windows header files from PHP. If someone could look at the PR I'd really appreciate it. Thanks! -- Chris Tankersley http://ctankersley.com