[llvm] [InstCombine] fold `ldexp(x, zext(i1 y))` to `fmul x, (select y, 2.0, 1.0)` (PR #94887)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

In a follow up could also handle sext -> 1.0 or 0.5 

https://github.com/llvm/llvm-project/pull/94887