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

[Stephen Tozer via cfe-commits]

SLTozer wrote:

> @SLTozer What's in patches 4 and 5...? I keep putting off looking at this stack, as I've been waiting for the whole series to appear (perhaps incorrectly)...

Patches 4 and 5 are less consequential, but I'll open them up - patch 4 is adding origin-tracking support to the IRBuilder, so that we properly track the origin of DebugLocs that have been assigned by the IRBuilder (rather than exclusively seeing the IRBuilder as the origin), and patch 5 updates `getMergedLocations` in the same way.

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