[Driver] Support libc++ in MSVC

Authored by phosek on Apr 28 2021, 11:23 AM.


[Driver] Support libc++ in MSVC

This implements support for using libc++ headers and library in the MSVC
toolchain. We only support libc++ that is a part of the toolchain, and
not headers installed elsewhere on the system.

Differential Revision: https://reviews.llvm.org/D101479