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

[Chandler Carruth via cfe-commits]

chandlerc wrote:

No worries about delay, this gives me a credible target to resolve the rest of the issues. I'll update this PR both to address review comments but also to try and address the rest of the failures. Appreciate runs to validate these updates. =]

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