[llvm] Reland [EquivClasses] Introduce members iterator-helper (PR #130319)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ml-opt-devrel-x86-64` running on `ml-opt-devrel-x86-64-b2` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/175/builds/14501

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

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM-Unit :: ADT/./ADTTests/12/26' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/b/ml-opt-devrel-x86-64-b1/build/unittests/ADT/./ADTTests-LLVM-Unit-1421065-12-26.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=26 GTEST_SHARD_INDEX=12 /b/ml-opt-devrel-x86-64-b1/build/unittests/ADT/./ADTTests
--

Script:
--
/b/ml-opt-devrel-x86-64-b1/build/unittests/ADT/./ADTTests --gtest_filter=EquivalenceClassesTest.MembersIterator
--
/b/ml-opt-devrel-x86-64-b1/llvm-project/llvm/unittests/ADT/EquivalenceClassesTest.cpp:80: Failure
Expected equality of these values:
  EC.members(EC.end()).begin()
    Which is: 8-byte object <78-B5 16-82 FE-7F 00-00>
  EC.member_end()
    Which is: 8-byte object <00-00 00-00 00-00 00-00>


/b/ml-opt-devrel-x86-64-b1/llvm-project/llvm/unittests/ADT/EquivalenceClassesTest.cpp:80
Expected equality of these values:
  EC.members(EC.end()).begin()
    Which is: 8-byte object <78-B5 16-82 FE-7F 00-00>
  EC.member_end()
    Which is: 8-byte object <00-00 00-00 00-00 00-00>



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


```

</details>

https://github.com/llvm/llvm-project/pull/130319