[libc] test bazel in presubmit

[nickdesaulniers]

llvm-libc breaks bazel builds a lot. Perhaps we could test this somewhat in presubmit. Should bazel be special here relative any other out of tree build system? idk, but perhaps llvm has a policy wrt bazel that I can review.

[llvmbot]

@llvm/issue-subscribers-libc

Author: Nick Desaulniers (nickdesaulniers)

llvm-libc breaks bazel builds a lot. Perhaps we could test this somewhat in presubmit. Should bazel be special here relative any other out of tree build system? idk, but perhaps llvm has a policy wrt bazel that I can review.

[dwblaikie]

Documented here: https://github.com/llvm/llvm-project/blob/main/utils/bazel/README.md
Which then links to here: https://llvm.org/docs/SupportPolicy.html#peripheral-tier

Specifically, the bazel build should not be the responsibility of non-bazel-interested contributors to maintain, fix, ensure it is not broken. It's by design that commits to LLVM will regularly break the bazel build & bazel-interested folks are expected to fix that after the fact, not burden contributors with having to include bazel fixes in the original changes.

[dwblaikie]

a presubmit that /doesn't/ interfere with the non-bazel-interested contributors flow, but notifies bazel-interested folks ahead of time so they can prepare a patch, etc, would be acceptable

[dwblaikie]

Or if you can configure the presubmit to only apply to bazel-interested folks, it can be blocking/error-ing for them, but not for other folks.

[nickdesaulniers]

cc @d0k