[llvm] Allow specifying libcxx builder image. (PR #110303)

[via llvm-commits]

EricWF wrote:

> > It looks like it's still failing with the latest run :-(
> 
> Argh that's unfortunate. How about we skip this test in libc++ CI to unblock this PR and I'll open a github issue to re-enable the test?
> 
> @EricWF It's probably easiest if you just add `--filter-out=TestDAP_subtleFrames.py` to the following LIT invocation as part of this PR:
> 
> https://github.com/llvm/llvm-project/blob/8c4bc1e75de27adfbaead34b895b0efbaf17bd02/libcxx/utils/ci/run-buildbot#L397
> 
> But if you prefer me doing it separately, let me know.

I have concerns about using the `run-buildbot` file to hide failing tests. I'll hold off on this change a little longer.



https://github.com/llvm/llvm-project/pull/110303