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

[Sergey Kachkov via llvm-commits]

skachkov-sc wrote:

@dyung thank you for the report! I've investigated the failures, the reason is that preserve-lcssa.ll doesn't require X86 target to be built, e.g.
```
c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\opt.exe: WARNING: failed to create target machine for 'x86_64-unknown-linux-gnu': unable to get target for 'x86_64-unknown-linux-gnu', see --version and --triple.
```
So loop-reduce works differently. I'll move my changes into separate LIT test with x86-registered-target requirement.

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