CPT: Add Build class and initial support for libc++ on Windows.
CPT: Add Build class and initial support for libc++ on Windows.

Build class can handle differences between Windows and Unix CMake.
libc++ on Windows is thoroughly untested.

Signed-off-by: Vassil Vassilev <0b291c0bdb4e22c8b7705ceedf8e168ff73f20e8@cern.ch>

karies/cling,karies/cling,karies/cling,karies/cling,root-mirror/cling,root-mirror/cling,marsupial/cling,marsupial/cling,karies/cling,root-mirror/cling,root-mirror/cling,marsupial/cling,root-mirror/cling,karies/cling,marsupial/cling,marsupial/cling,root-mirror/cling,marsupial/cling