MSVC_VERSION
------------
The version of Microsoft Visual C/C++ being used if any.
Known version numbers are::
1200 = VS 6.0
1300 = VS 7.0
1310 = VS 7.1
1400 = VS 8.0
1500 = VS 9.0
1600 = VS 10.0
1700 = VS 11.0
1800 = VS 12.0
1900 = VS 14.0