[zorg] Proposal: Add options allowing MSVC builds with Clang Cmake Build Factory.

[Rick Foos]

I'm final testing a patch that allows getClangCMakeBuildFactory to 
become a more unified builder per earlier discussions with Renato.

The upgrades allow:
1) Builds with cmake generators 'Visual Studio 12', 'Ninja', 'Unix 
Makefiles' by changing arguments.
2) Builds on Linux w/o modifications (defaults remain the same)
3) Builds on Windows with modified arguments.
3a) Windows builds use basically the same arguments as Linux with mods 
for MSVC.
4) Optional stage 2 cmake build using built clang with different 
generator and options. This allows an MSVC build followed by a clang 
built clang per the selfhosting logic.

Does this sound like a reasonable set of features to upgrade 
getClangCMakeBuildFactory?

Rick