[llvm] [RuntimeLibcalls] Use a multiclass for all libm impls (NFC) (PR #148349)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

Can you rebase this?

The main thing I'm iffy on is I would like to start grouping libcalls by named sets of the provider, and version. i.e., I would like to group libm calls + type + introduced c version + platform specific stuff like msvc dropping random functions 

https://github.com/llvm/llvm-project/pull/148349