[llvm] [X86] Lower mathlib call ldexp into scalef when avx512 is enabled (PR #69710)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

Closing this abandoned PR and adding a issue (#165694) to track future work - I'll add the test coverage from this patch to trunk so we have something to work from.

https://github.com/llvm/llvm-project/pull/69710