[clang] [llvm] [DLCov 3/5] Implement DebugLoc origin-tracking (PR #107369)

[Stephen Tozer via cfe-commits]

SLTozer wrote:

> IIRC, there are still some open review threads in this PR, mainly related to reducing duplication in the symbolication bits.

Yes, this part won't land quite yet; as I'm kicking these reviews back into action, I'll be pushing up some other reviews to come before this one in the patch stack. The origin-tracking feature here is very useful for actually triaging bugs, but the most important features to land first are enabling coverage-tracking in its entirety, including annotating existing sites in the compiler, so I'll be coming back to this patch after landing the remaining coverage-focused patches.

https://github.com/llvm/llvm-project/pull/107369