[llvm] [InstCombine] Fold more 'fcmp' 'select' instrs idioms into 'fabs' (PR #83381)

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sushgokh wrote:

>Testing multiple passes at once is generally discouraged. The test that I'd expect to see here is just that SROA propagates no-signed-zeros-fp-math to the generated PHI, given that we should have tests for the instcombine select/phi working elsewhere.

I had a test that showed transformation after the passes but this is what @jcranmer-intel suggested. So, I just have a test with SROA transform. 

https://github.com/llvm/llvm-project/pull/83381