[llvm] [LLVM][Support] Add getTrailingObjects() for single trailing type (PR #138970)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-aarch64-darwin` running on `doug-worker-4` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/190/builds/19745

<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 'Clang-Unit :: ./AllClangUnitTests/14/48' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/Users/buildbot/buildbot-root/aarch64-darwin/build/tools/clang/unittests/./AllClangUnitTests-Clang-Unit-94132-14-48.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=48 GTEST_SHARD_INDEX=14 /Users/buildbot/buildbot-root/aarch64-darwin/build/tools/clang/unittests/./AllClangUnitTests
--

Note: This is test shard 15 of 48.
[==========] Running 510 tests from 105 test suites.
[----------] Global test environment set-up.
[----------] 1 test from MinimizeSourceToDependencyDirectivesTest
[ RUN      ] MinimizeSourceToDependencyDirectivesTest.DefineMultilineArgsStringize
[       OK ] MinimizeSourceToDependencyDirectivesTest.DefineMultilineArgsStringize (2 ms)
[----------] 1 test from MinimizeSourceToDependencyDirectivesTest (2 ms total)

[----------] 1 test from HeaderSearchTest
[ RUN      ] HeaderSearchTest.Dots
[       OK ] HeaderSearchTest.Dots (4 ms)
[----------] 1 test from HeaderSearchTest (4 ms total)

[----------] 1 test from ModuleDeclStateTest
[ RUN      ] ModuleDeclStateTest.NotModule
[       OK ] ModuleDeclStateTest.NotModule (4 ms)
[----------] 1 test from ModuleDeclStateTest (4 ms total)

[----------] 1 test from DxcModeTest
[ RUN      ] DxcModeTest.TargetProfileValidation
[       OK ] DxcModeTest.TargetProfileValidation (11 ms)
[----------] 1 test from DxcModeTest (11 ms total)

[----------] 1 test from MultilibTest
[ RUN      ] MultilibTest.SetPushback
[       OK ] MultilibTest.SetPushback (0 ms)
[----------] 1 test from MultilibTest (0 ms total)

[----------] 2 tests from ExprMutationAnalyzerTest
[ RUN      ] ExprMutationAnalyzerTest.CallUnresolved
[       OK ] ExprMutationAnalyzerTest.CallUnresolved (68 ms)
[ RUN      ] ExprMutationAnalyzerTest.RangeForNonArrayByConstRef
input.cc:1:103: warning: expression result unused [-Wunused-value]
    1 | struct V { const int* begin() const; const int* end() const; };void f() { V x; for (const int& e : x) e; }
      |                                                                                                       ^
[       OK ] ExprMutationAnalyzerTest.RangeForNonArrayByConstRef (3 ms)
[----------] 2 tests from ExprMutationAnalyzerTest (71 ms total)

[----------] 1 test from MacroExpansionContextTest
[ RUN      ] MacroExpansionContextTest.StringizingVariadicMacros
[       OK ] MacroExpansionContextTest.StringizingVariadicMacros (0 ms)
[----------] 1 test from MacroExpansionContextTest (0 ms total)

[----------] 1 test from EnvironmentTest
...

```

</details>

https://github.com/llvm/llvm-project/pull/138970