[llvm] [DAGCombine] Transform `shl X, cttz(Y)` to `mul (Y & -Y), X` if cttz is unsupported (PR #85066)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

Can you also port the same to globalisel? 

https://github.com/llvm/llvm-project/pull/85066