[llvm] Fill in some missing C23 math libcall handling (PR #170672)

[Nikita Popov via llvm-commits]

nikic wrote:

Nearly all changes here look orthogonal to me, there should be not need for stacked PRs.

Note that LLVM always uses squash merge, so you can't break things down by commit, it has to be by PRs.

https://github.com/llvm/llvm-project/pull/170672