Substitute LLVM's version into the msbuild property file at config time

Requires shuffling the CPack code up before add_subdirectory(tools), but
that's where the version settings are anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189615 91177308-0d34-0410-b5e6-96231b3b80d8