[clang-cl] Add support for /Brepro

The /Brepro flag controls whether or not the compiler should embed
timestamps into the object file.  Object files which do not embed
timestamps are not suitable for incremental linking but are suitable for
hermetic build systems and staged self-hosts of clang.

A normal clang spelling of this flag has been added,
-mincremental-linker-compatible.

llvm-svn: 256204