[llvm] [LLVM] Slay undead copysign code (PR #111269)

[via llvm-commits]

workingjubilee wrote:

@arsenm I see. If you can coach me on some of the finer points of making a `.td` (I have the basic gist, but there will be some questions), I'd be happy to assemble something such that the data covered in those two files is in a tablegen, in a followup. Then I will be able to make sure that it or another file is supplied with the necessary information that frontends... frontends that aren't clang, anyways... need. And then it will cover libm _properly_, instead of the current state of affairs.

https://github.com/llvm/llvm-project/pull/111269