[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 `openmp-offload-sles-build-only` running on `rocm-worker-hw-04-sles` while building `llvm` at step 8 "Add check check-llvm".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/140/builds/18506

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

```
Step 8 (Add check check-llvm) failure: test (failure)
******************** TEST 'LLVM-Unit :: ADT/./ADTTests/12/52' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.build/unittests/ADT/./ADTTests-LLVM-Unit-1920373-12-52.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=52 GTEST_SHARD_INDEX=12 /home/botworker/bbot/builds/openmp-offload-sles-build/llvm.build/unittests/ADT/./ADTTests
--

Script:
--
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.build/unittests/ADT/./ADTTests --gtest_filter=EquivalenceClassesTest.MembersIterator
--
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/unittests/ADT/EquivalenceClassesTest.cpp:80: Failure
Expected equality of these values:
  EC.members(EC.end()).begin()
    Which is: 8-byte object <68-D5 A4-68 FE-7F 00-00>
  EC.member_end()
    Which is: 8-byte object <00-00 00-00 00-00 00-00>


/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/unittests/ADT/EquivalenceClassesTest.cpp:80
Expected equality of these values:
  EC.members(EC.end()).begin()
    Which is: 8-byte object <68-D5 A4-68 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