[clang] [compiler-rt] [clang][UBSan] Add implicit conversion check for bitfields (PR #75481)

[Richard Smith via cfe-commits]

zygoloid wrote:

I don't think we've established an explicit policy, and we've made ABI-breaking changes previously. I think we should avoid breaks within a major release version (don't backport this) to avoid giving packagers headaches: the ubsan runtime is installed in a versioned directory, but I don't think that includes the patch version.

Having an ABI break here seems OK and in line with historic precedent. (But we ought to document our ABI policy for our runtime libraries.)

https://github.com/llvm/llvm-project/pull/75481