[clang] [Clang] Fix assertion failure when classifying a dependent call to a builtin (PR #210524)

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github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Windows-->
# :window: Windows x64 Test Results

* 55771 tests passed
* 1404 tests skipped
* 1 test failed

## Failed Tests
(click on a test name to see its output)

### Clang-Unit
<details>
<summary>Clang-Unit._/AllClangUnitTests_exe/SourceCodeTest/GetCallReturnType_DependentBuiltinCall</summary>

```
Script:
--
C:\_work\llvm-project\llvm-project\build\tools\clang\unittests\.\AllClangUnitTests.exe --gtest_filter=SourceCodeTest.GetCallReturnType_DependentBuiltinCall
--
C:\_work\llvm-project\llvm-project\clang\unittests\Tooling\SourceCodeTest.cpp:866
Value of: SawBuiltinFnCallee
  Actual: false
Expected: true


```
</details>

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the `infrastructure` label.

https://github.com/llvm/llvm-project/pull/210524