[clang] [clang][DebugInfo] Store current location metadata in CGDebugInfo (PR #193918)

[Jeremy Morse via cfe-commits]

https://github.com/jmorse approved this pull request.

LGTM. This means we'll be leaning on state a little more, with the risk of something getting stale, but I guess that's the trade-off for these optimisations.

An entirely optional extra bit of validation would be building stage2-clang with/without this patch and seeing whether it builds an identical binary -- that usually sets my mind at rest that there aren't any other sneek paths that are getting stale state. (Not necessary to land IMO).

https://github.com/llvm/llvm-project/pull/193918