[llvm] [SDAG] Fix deferring constrained function calls (PR #153029)

[Kevin P. Neal via llvm-commits]

kpneal wrote:

No, my question was considering the case where SDAG is working on a basic block containing a function call that calls a function that changes the rounding mode. BB->foo()->bar()->changes the rounding mode(). I don't think we can model that.

https://github.com/llvm/llvm-project/pull/153029