Successful build of Python 2.7.10 with clang-cl 3.6.1

Python now builds with clang 3.6.1 on Windows. The trick was to patch the visual studio project files so that only the 64-bit configuration refers to clang. I ended up writing a Python script to do the patching:

https://github.com/russellw/pyxi/blob/master/patch-vcxproj.py