[llvm] Revert "[InstCombine] Teach foldSelectOpOp about samesign" (PR #124123)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon commented:

I don't think #122723 is problematic per-se, but I think it exposed an underlying problem: I need more time to investigate. However, I think the revert is okay while we investigate the problem, but would defer to @nikic on the final approval.

https://github.com/llvm/llvm-project/pull/124123