3fe8ec7906
This reverts commit 7c349c369847dc2f1736efb9c90d03521cd44a90. Per discussion at https://reviews.llvm.org/rG7c349c369847dc2f1736efb9c90d03521cd44a90 and elsewhere, the lowering to LLVM defined here isn't what it should be and the fastmath flag usage isn't correct, so `arith.is_nan` and `arith.is_inf` cannot exist in their current form. It's unclear if those operations should be introduced in the future, since they make the dialect more complex and don't add any expressive power. Further discussion may be moved to an RFC (or I'll drop this patch). Differential Revision: https://reviews.llvm.org/D157543