[clang] [clang] Track final substitution for Subst* AST nodes (PR #132748)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

@thurstond Well can you provide a more recent buildbot failure link where https://github.com/llvm/llvm-project/pull/130182 is not on the list of possible culpirits? Because the link @fmayer provided for sure included it.

https://github.com/llvm/llvm-project/pull/132748