[llvm] [InstCombine] Enable select freeze poison folding when storing value (PR #129776)

[John McIver via llvm-commits]

jmciver wrote:

I refactored the select fold into helper getValueReplacement, which can make use of the freeze argument test in the caller: `match(Op0, m_Undef())`. The isGuaranteedNotToBeUndefOrPoison call is located in the lambda body. Multi-use
freeze instruction are not common so the execution impact should be generally low, but the readability is improved.


https://github.com/llvm/llvm-project/pull/129776