[llvm] [AMDGPU] Add FastMathFlags::intersectValue helper for rsq ninf/nsz fix (PR #217724)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-armv8-quick` running on `linaro-clang-armv8-quick` while building `llvm` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/154/builds/36089

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

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'LLVM-Unit :: Support/./SupportTests/217/454' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/Support/./SupportTests-LLVM-Unit-204978-217-454.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=454 GTEST_SHARD_INDEX=217 /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/Support/./SupportTests
--

Script:
--
/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/unittests/Support/./SupportTests --gtest_filter=ProgramEnvTest.TestLockFileExclusive
--
/home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/unittests/Support/ProgramTest.cpp:648: Failure
Value of: Finished
  Actual: false
Expected: true


/home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/unittests/Support/ProgramTest.cpp:648
Value of: Finished
  Actual: false
Expected: true



********************


```

</details>

https://github.com/llvm/llvm-project/pull/217724