[clang] Reland "[clang][modules-driver] Add support for C++ named modules and import std" (2nd attempt) (PR #194475)

[Naveen Seth Hanig via cfe-commits]

naveen-seth wrote:

Fix in 2nd commit of this PR.
This is the 2nd attempt at relanding and if we fail build-bot tests again without any output, I'll remove `clang/test/Driver/modules-driver-import-std.cpp` and reland that test later separately.

https://github.com/llvm/llvm-project/pull/194475