[llvm] [ConstantFolding] Add ilogb in isMathLibCallNoop (PR #122582)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm approved this pull request.

LGTM. We probably should use an explicit triple in the test though (I have a WIP patch to switch the default handling to assume no libcalls are available without a triple) 

https://github.com/llvm/llvm-project/pull/122582