[llvm] [llvm-lto2] Added llvm-lto2 -unified-lto descriptions (revised) (PR #155462)

[Faith Rivera via llvm-commits]

fnriv wrote:

Hi, 

I had a mac machine when developing this and currently do not have access to a Windows/Linux machine

An alternative approach I can change could be to revert it to string checking rather than clEnumValN checking (as was done before)? I had changed it to clEnumValN due to precedence of that type of check (you can see conversation about this in #148309 

https://github.com/llvm/llvm-project/pull/155462