Require CMake 2.8.12.1 or later on Windows

That version knows to use the /FS flag, which is needed for building
lib/interception with VS2013.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@201184 91177308-0d34-0410-b5e6-96231b3b80d8