[clang] Patch series to reapply #118734 and substantially improve it (PR #120534)

[Chandler Carruth via cfe-commits]

chandlerc wrote:

@dyung -- Ok, my latest attempt to work around these MSVC issues is now pushed to this PR. It also contains a commit of specifically debugging hacks to try and extract more information from any failure here. If you could try doing another build with the latest commit ([2ec750d](https://github.com/llvm/llvm-project/pull/120534/commits/2ec750d0105e1d4d52791f85293d16d28f6ccbd8)) in this PR, would be very interested in how it works.

https://github.com/llvm/llvm-project/pull/120534