[llvm] [DataLayout] Add byte specification (PR #106536)

[Alexander Richardson via llvm-commits]

https://github.com/arichardson commented:

In general this looks fine to me but I'll defer to others about whether this is the correct strategy towards non-8-bit bytes.

Personally, I much prefer having code upstream that is testable rather than just a fixes upstream that can only be tested downstream (this has been a notable issue for CHERI where each upstream merge brings in new test failures), so I like having this upstream.

https://github.com/llvm/llvm-project/pull/106536