[clang] [clang] Migrate away from PointerUnion::dyn_cast (NFC) (PR #228843)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lldb-arm-ubuntu` running on `linaro-lldb-arm-ubuntu` while building `clang` at step 6 "test".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/18/builds/27323

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

```
Step 6 (test) failure: build (failure)
...
PASS: lldb-api :: functionalities/thread/step_until/TestStepUntil.py (796 of 3012)
PASS: lldb-api :: functionalities/thread/step_until/TestStepUntilAPI.py (797 of 3012)
PASS: lldb-api :: functionalities/thread/thread_exit/TestThreadExit.py (798 of 3012)
SKIPPED: lldb-api :: functionalities/tsan/basic/TestTsanBasic.py (799 of 3012)
SKIPPED: lldb-api :: functionalities/tsan/cpp_global_location/TestTsanCPPGlobalLocation.py (800 of 3012)
PASS: lldb-api :: functionalities/thread_plan/TestThreadPlanCommands.py (801 of 3012)
PASS: lldb-api :: functionalities/thread_plan/step_over_breakpoint_site/TestStepOverBreakpointSite.py (802 of 3012)
SKIPPED: lldb-api :: functionalities/tsan/global_location/TestTsanGlobalLocation.py (803 of 3012)
UNSUPPORTED: lldb-api :: functionalities/tsan/multiple/TestTsanMultiple.py (804 of 3012)
PASS: lldb-api :: functionalities/thread/exit_during_expression/TestExitDuringExpression.py (805 of 3012)
FAIL: lldb-api :: functionalities/thread/exit_during_step/TestExitDuringStep.py (806 of 3012)
******************** TEST 'lldb-api :: functionalities/thread/exit_during_step/TestExitDuringStep.py' FAILED ********************
Script:
--
/usr/bin/python3.10 /home/tcwg-buildbot/worker/lldb-arm-ubuntu/llvm-project/lldb/test/API/dotest.py -u CXXFLAGS -u CFLAGS --env LLVM_LIBS_DIR=/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./lib --env LLVM_INCLUDE_DIR=/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/include --env LLVM_TOOLS_DIR=/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./bin --triple armv8l-unknown-linux-gnueabihf --build-dir /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/lldb-test-build --lldb-module-cache-dir /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/lldb-test-build/module-cache-lldb/lldb-api --clang-module-cache-dir /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/lldb-test-build/module-cache-clang/lldb-api --executable /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./bin/lldb --lldb-python-dir /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/local/lib/python3.10/dist-packages --compiler /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./bin/clang --dsymutil /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./bin/dsymutil --make /usr/bin/gmake --llvm-tools-dir /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./bin --lldb-obj-root /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/tools/lldb --lldb-libs-dir /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/./lib --cmake-build-type Release /home/tcwg-buildbot/worker/lldb-arm-ubuntu/llvm-project/lldb/test/API/functionalities/thread/exit_during_step -p TestExitDuringStep.py --timeout 600
--
Exit Code: 1

Command Output (stdout):
--
Skipping the following test categories: libc++, msvcstl, dsym, pdb, gmodules, debugserver, objc

--
Command Output (stderr):
--
UNSUPPORTED: LLDB (/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/bin/clang-arm) :: test_dsym (TestExitDuringStep.ExitDuringStepTestCase) (test case does not fall in any category of interest for this run) 
PASS: LLDB (/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/bin/clang-arm) :: test_dwarf (TestExitDuringStep.ExitDuringStepTestCase)
FAIL: LLDB (/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/bin/clang-arm) :: test_dwo (TestExitDuringStep.ExitDuringStepTestCase)
Log Files:
 - /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/lldb-test-build/functionalities/thread/exit_during_step/TestExitDuringStep.dwo/Failure_test_dwo.log
UNSUPPORTED: LLDB (/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/bin/clang-arm) :: test_step_in_dsym (TestExitDuringStep.ExitDuringStepTestCase) (test case does not fall in any category of interest for this run) 
PASS: LLDB (/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/bin/clang-arm) :: test_step_in_dwarf (TestExitDuringStep.ExitDuringStepTestCase)
FAIL: LLDB (/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/bin/clang-arm) :: test_step_in_dwo (TestExitDuringStep.ExitDuringStepTestCase)
Log Files:
 - /home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/lldb-test-build/functionalities/thread/exit_during_step/TestExitDuringStep.dwo/Failure_test_step_in_dwo.log
UNSUPPORTED: LLDB (/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/bin/clang-arm) :: test_step_over_dsym (TestExitDuringStep.ExitDuringStepTestCase) (test case does not fall in any category of interest for this run) 
PASS: LLDB (/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/bin/clang-arm) :: test_step_over_dwarf (TestExitDuringStep.ExitDuringStepTestCase)
PASS: LLDB (/home/tcwg-buildbot/worker/lldb-arm-ubuntu/build/bin/clang-arm) :: test_step_over_dwo (TestExitDuringStep.ExitDuringStepTestCase)
======================================================================
FAIL: test_dwo (TestExitDuringStep.ExitDuringStepTestCase)
   Test thread exit during step handling.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/tcwg-buildbot/worker/lldb-arm-ubuntu/llvm-project/lldb/packages/Python/lldbsuite/test/lldbtest.py", line 2206, in test_method
    return attrvalue(self)
  File "/home/tcwg-buildbot/worker/lldb-arm-ubuntu/llvm-project/lldb/test/API/functionalities/thread/exit_during_step/TestExitDuringStep.py", line 21, in test
    self.exit_during_step_base(
  File "/home/tcwg-buildbot/worker/lldb-arm-ubuntu/llvm-project/lldb/test/API/functionalities/thread/exit_during_step/TestExitDuringStep.py", line 100, in exit_during_step_base
    self.assertGreaterEqual(

```

</details>

https://github.com/llvm/llvm-project/pull/228843