[clang] fix: constexpr bit_cast with empty base classes (PR #82383)

[via cfe-commits]

sethp wrote:

Ah, got it, thank you: I am once again wishing for a `.gitattributes` "keep both" merge strategy more usable than `union` for the release notes.

> Do you not have the necessary permissions to merge it yourself?

No, I don't have write permissions on the LLVM repo: I think I will need one of y'all's help hitting the button here. I'll look into getting permissions, too, but I presume there's some steps involved.

https://github.com/llvm/llvm-project/pull/82383