[llvm] [Target] Add "override" where appropriate (NFC) (PR #165083)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64le-flang-rhel-clang` running on `ppc64le-flang-rhel-test` while building `llvm` at step 6 "test-build-unified-tree-check-flang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/157/builds/41897

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

```
Step 6 (test-build-unified-tree-check-flang) failure: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
10.109 [4/29/0] cd /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/runtimes/runtimes-bins && /home/buildbots/llvm-external-buildbots/cmake-3.31.2/bin/cmake --build /home/buildbots/llvm-external-buildbots/workers/ppc64le-flang-rhel-test/ppc64le-flang-rhel-clang-build/build/runtimes/runtimes-bins/ --target libomp-mod --config Release
ninja: no work to do.
10.328 [3/6/25] Building CXX object tools/flang/unittests/Optimizer/CMakeFiles/FlangOptimizerTests.dir/RTBuilder.cpp.o
11.037 [2/5/27] Linking CXX executable tools/flang/unittests/Common/FlangCommonTests
14.952 [2/4/28] Linking CXX executable tools/flang/unittests/Optimizer/FlangOptimizerTests
139.452 [2/3/29] Building CXX object tools/flang/unittests/Frontend/CMakeFiles/FlangFrontendTests.dir/CodeGenActionTest.cpp.o
173.821 [2/2/30] Building CXX object tools/flang/unittests/Frontend/CMakeFiles/FlangFrontendTests.dir/CompilerInstanceTest.cpp.o
209.162 [2/1/31] Building CXX object tools/flang/unittests/Frontend/CMakeFiles/FlangFrontendTests.dir/FrontendActionTest.cpp.o
271.333 [1/1/32] Linking CXX executable tools/flang/unittests/Frontend/FlangFrontendTests
271.335 [0/1/32] Running the Flang regression tests
command timed out: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1472.144633

```

</details>

https://github.com/llvm/llvm-project/pull/165083