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

[Matt Arsenault via llvm-commits]

arsenm wrote:

Regardless of the usage, I think these should still be recorded in RuntimeLibcalls. Ideally it would be a complete database of all calls for the system, not just used 

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