[llvm] [ConstantFolding] Add flag to disable call folding (PR #140270)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

If we want such a debugging flag, I think this is the wrong heuristic. I would be more interesting in a way of disabling folding of any calls that go through the host library. Not folding exact functions we directly and correctly implement in APFloat is silly 

https://github.com/llvm/llvm-project/pull/140270