[llvm] [DAGCombiner] Relax nsz constraint for FP optimizations (PR #165011)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64le-mlir-rhel-clang` running on `ppc64le-mlir-rhel-test` while building `llvm` at step 6 "test-build-check-mlir-build-only-check-mlir".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/129/builds/34644

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-check-mlir-build-only-check-mlir) failure: 1200 seconds without output running [b'ninja', b'check-mlir'], attempting to kill
...
PASS: MLIR-Unit :: Interfaces/./MLIRInterfacesTests/13/22 (3731 of 3742)
PASS: MLIR :: mlir-runner/verify-entry-point.mlir (3732 of 3742)
PASS: MLIR-Unit :: IR/./MLIRIRTests/0/131 (3733 of 3742)
PASS: MLIR-Unit :: Interfaces/./MLIRInterfacesTests/12/22 (3734 of 3742)
PASS: MLIR-Unit :: Interfaces/./MLIRInterfacesTests/11/22 (3735 of 3742)
PASS: MLIR-Unit :: Pass/./MLIRPassTests/10/13 (3736 of 3742)
PASS: MLIR :: Pass/ir-printing-file-tree.mlir (3737 of 3742)
PASS: MLIR :: mlir-tblgen/op-error.td (3738 of 3742)
PASS: MLIR :: Pass/pipeline-options-parsing.mlir (3739 of 3742)
PASS: MLIR :: mlir-reduce/dce-test.mlir (3740 of 3742)
command timed out: 1200 seconds without output running [b'ninja', b'check-mlir'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=2263.675975

```

</details>

https://github.com/llvm/llvm-project/pull/165011