[llvm] [TLI] Add support for nan libfunc (PR #101356)

[Joshua Cranmer via llvm-commits]

jcranmer-intel wrote:

Looking at this patch prompts me of this related thought: maybe we should have a helper macro for floating-point functions that can define all the relevant suffixes, as Annex H adds like a bajillion more suffixed variants here?

Not that this blocks this PR, just food for thought for the future

https://github.com/llvm/llvm-project/pull/101356