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

[Yashwant Singh via llvm-commits]

yashssh wrote:

The original inspiration for the missed optimization can be seen here https://godbolt.org/z/z3Es5oxqv. 
This seemed to be the most straightforward way to achieve this optimization and a detailed discussion about the issue and why this fold was skipped by 'instcombine' is documented here #51601 


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