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

[Kevin P. Neal via llvm-commits]

kpneal wrote:

Rounding mode can be changed by an arbitrary function called from inside a basic block. Thus, we can't model it perfectly and need to take it into account when reordering.

And I still think tests are worthwhile even if all they do is demonstrate a bug. It seems like a good comment on the issue including a FIXME and perhaps a link to a bug report would be helpful. Do we have a stated policy on this?

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