[clang] Thread Safety Analysis: Don't warn at joins that re-branch on a try-lock result (PR #209796)

[Marco Elver via cfe-commits]

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

LGTM.

The CI has some failures though, but I think from unrelated tests - can you rebase? Then we can rerun CI.

https://github.com/llvm/llvm-project/pull/209796