[lld] [lld] Migrate away from PointerUnion::{is, get} (NFC) (PR #119993)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lldb-x86_64-debian` running on `lldb-x86_64-debian` while building `lld` at step 6 "test".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/162/builds/12561

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

```
Step 6 (test) failure: build (failure)
...
PASS: lldb-api :: tools/lldb-server/TestGdbRemoteProcessInfo.py (24 of 2728)
PASS: lldb-api :: tools/lldb-server/attach-wait/TestGdbRemoteAttachWait.py (25 of 2728)
PASS: lldb-api :: tools/lldb-server/TestGdbRemoteExpeditedRegisters.py (26 of 2728)
PASS: lldb-api :: commands/expression/multiline-completion/TestMultilineCompletion.py (27 of 2728)
PASS: lldb-api :: tools/lldb-server/vCont-threads/TestSignal.py (28 of 2728)
PASS: lldb-api :: commands/gui/basic/TestGuiBasic.py (29 of 2728)
PASS: lldb-api :: functionalities/load_unload/TestLoadUnload.py (30 of 2728)
PASS: lldb-api :: tools/lldb-dap/variables/TestDAP_variables.py (31 of 2728)
PASS: lldb-api :: commands/gui/viewlarge/TestGuiViewLarge.py (32 of 2728)
PASS: lldb-api :: commands/watchpoints/watchpoint_set_command/TestWatchLocationWithWatchSet.py (33 of 2728)
FAIL: lldb-api :: tools/lldb-dap/launch/TestDAP_launch.py (34 of 2728)
******************** TEST 'lldb-api :: tools/lldb-dap/launch/TestDAP_launch.py' FAILED ********************
Script:
--
/usr/bin/python3 /home/worker/2.0.1/lldb-x86_64-debian/llvm-project/lldb/test/API/dotest.py -u CXXFLAGS -u CFLAGS --env LLVM_LIBS_DIR=/home/worker/2.0.1/lldb-x86_64-debian/build/./lib --env LLVM_INCLUDE_DIR=/home/worker/2.0.1/lldb-x86_64-debian/build/include --env LLVM_TOOLS_DIR=/home/worker/2.0.1/lldb-x86_64-debian/build/./bin --arch x86_64 --build-dir /home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex --lldb-module-cache-dir /home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex/module-cache-lldb/lldb-api --clang-module-cache-dir /home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex/module-cache-clang/lldb-api --executable /home/worker/2.0.1/lldb-x86_64-debian/build/./bin/lldb --compiler /home/worker/2.0.1/lldb-x86_64-debian/build/./bin/clang --dsymutil /home/worker/2.0.1/lldb-x86_64-debian/build/./bin/dsymutil --make /usr/bin/make --llvm-tools-dir /home/worker/2.0.1/lldb-x86_64-debian/build/./bin --lldb-obj-root /home/worker/2.0.1/lldb-x86_64-debian/build/tools/lldb --lldb-libs-dir /home/worker/2.0.1/lldb-x86_64-debian/build/./lib -t /home/worker/2.0.1/lldb-x86_64-debian/llvm-project/lldb/test/API/tools/lldb-dap/launch -p TestDAP_launch.py
--
Exit Code: 1

Command Output (stdout):
--
lldb version 20.0.0git (https://github.com/llvm/llvm-project.git revision e04fde193bc2acbaf3ece851479fbd9928c1e280)
  clang revision e04fde193bc2acbaf3ece851479fbd9928c1e280
  llvm revision e04fde193bc2acbaf3ece851479fbd9928c1e280
Skipping the following test categories: ['libc++', 'dsym', 'gmodules', 'debugserver', 'objc']
========= DEBUG ADAPTER PROTOCOL LOGS =========
1734235730.218882084 --> 
Content-Length: 344

{
  "arguments": {
    "adapterID": "lldb-native",
    "clientID": "vscode",
    "columnsStartAt1": true,
    "linesStartAt1": true,
    "locale": "en-us",
    "pathFormat": "path",
    "sourceInitFile": false,
    "supportsRunInTerminalRequest": true,
    "supportsStartDebuggingRequest": true,
    "supportsVariablePaging": true,
    "supportsVariableType": true
  },
  "command": "initialize",
  "seq": 1,
  "type": "request"
}
1734235730.221407413 <-- 
Content-Length: 1589


```

</details>

https://github.com/llvm/llvm-project/pull/119993