[llvm] [LSR] Do not create duplicated PHI nodes while preserving LCSSA form (PR #107380)

[via llvm-commits]

dyung wrote:

The test preserve-lcssa.ll is failing on several bots, can you investigate and revert if you need time to investigate?
- https://lab.llvm.org/buildbot/#/builders/190/builds/5231
- https://lab.llvm.org/buildbot/#/builders/161/builds/1855

https://github.com/llvm/llvm-project/pull/107380