This version updates the clang cmake factory so that it can be used for both Linux and Windows MSVC builders.
It successfully builds and tests with Visual Studio 2013.
An original update to the MSVC builder was dropped after discussion with Renato for this method. The is better than the first patch, and this is close to a common cmake factory for other projects besides clang.
The only addition to allow this to expand to other projects is the ability to check out different source trees.
This also enables two new builders that use this script.