[llvm] [X86] Use RORX over SHR imm (PR #77964)

[Shengchen Kan via llvm-commits]

https://github.com/KanRobert requested changes to this pull request.

Sorry for request change on this. I have two concerns here
1.  Whether this change will bring benefits is questionable b/c
      a.  it introduces false dependency 
      b.  code size of RORX is longer than SHR
2.  it's probably not the best solution to do this by adding new pattern. This 
      optimization should occur at most when there is a user in the previously generated 
      EFLAGS. 

https://github.com/llvm/llvm-project/pull/77964