[llvm] [InstCombine] Do not simplify lshr/shl arg if it is part of fshl rotate pattern. (PR #66115)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon commented:

A couple of minors - try to use m_Specific instead of matching the operand values afterward

https://github.com/llvm/llvm-project/pull/66115