[llvm] [Bazel] Export compiler-rt builtins sources (PR #157200)

[Chandler Carruth via llvm-commits]

https://github.com/chandlerc commented:

Thanks for the review!

Note that in testing I discovered I needed to do something similar for the header-only SipHash used by some of the builtins. PTAL if you can?

> Do keep in mind that the wide globs could lead to accidentally "overincluding" files in the future which might lead to bugs that are harder to track down than more obvious "missing file" bugs which can fairly easily be fixed via visual comparison to the CMake sources. Not sure what the better tradeoff is.

Well, in working with an explicit list for a few years downstream, we have definitely ended up with missing files that went unnoticed. So I think at least initially that motivates using the globs.

When initially building this version, I ended up on several cases having overly broad globs and most (but not all) were easily caught due to failing to build for the relevant target platform. So I'm hopeful that this tradeoff works well in practice, but certainly happy for us to revisit if over-inclusion becomes a problem.

https://github.com/llvm/llvm-project/pull/157200