[clang] [llvm] Reland "[DebugMetadata][DwarfDebug] Support function-local types in lexical block scopes (4/7)" (PR #165032)

[Jeremy Morse via cfe-commits]

https://github.com/jmorse commented:

Looked at the tests; only thing I've missed now is the unittests (out of time today).

funcimport-debug-retained-nodes.ll is enjoyably thorough -- I wonder whether it's so specific that it'll easily lose coverage of what it's testing though. Sometimes we use `-debug` output to ensure we're taking the correct codepath, would it be feasible to check that to ensure we're hitting the lazy-metadata-loading path? (This is usually discouraged, but given how hard it is to debug this area, IMO it's worth doing to avoid future quiet loss of coverage)

https://github.com/llvm/llvm-project/pull/165032