[clang] Avoid assert in substqualifier (PR #182707)

[via cfe-commits]

github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Linux-->
# :penguin: Linux x64 Test Results

* 86970 tests passed
* 1321 tests skipped
* 2 tests failed

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

### Clang
<details>
<summary>Clang.Frontend/verify-marker.c</summary>

```
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
/home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/clang -cc1 -internal-isystem /home/gha/actions-runner/_work/llvm-project/llvm-project/build/lib/clang/23/include -nostdsysteminc -verify /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/Frontend/verify-marker.c
# executed command: /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/clang -cc1 -internal-isystem /home/gha/actions-runner/_work/llvm-project/llvm-project/build/lib/clang/23/include -nostdsysteminc -verify /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/Frontend/verify-marker.c
# .---command stderr------------
# | error: 'expected-error' diagnostics expected but not seen: 
# |   File /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/Frontend/verify-marker.c Line 6 (directive at /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/Frontend/verify-marker.c:7): redefinition of 'x'
# | error: 'expected-note' diagnostics expected but not seen: 
# |   File /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/Frontend/verify-marker.c Line 5 (directive at /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/Frontend/verify-marker.c:8): previous
# | 2 errors generated.
# `-----------------------------
# error: command failed with exit status: 1

--

```
</details>
<details>
<summary>Clang.SemaCXX/cxx1z-init-statement.cpp</summary>

```
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
/home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/clang -cc1 -internal-isystem /home/gha/actions-runner/_work/llvm-project/llvm-project/build/lib/clang/23/include -nostdsysteminc -std=c++1z -Wno-unused-value -verify /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/SemaCXX/cxx1z-init-statement.cpp
# executed command: /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/clang -cc1 -internal-isystem /home/gha/actions-runner/_work/llvm-project/llvm-project/build/lib/clang/23/include -nostdsysteminc -std=c++1z -Wno-unused-value -verify /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/SemaCXX/cxx1z-init-statement.cpp
# .---command stderr------------
# | error: 'expected-error' diagnostics expected but not seen: 
# |   File /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/SemaCXX/cxx1z-init-statement.cpp Line 55: redefinition of 'a'
# | error: 'expected-note' diagnostics expected but not seen: 
# |   File /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/SemaCXX/cxx1z-init-statement.cpp Line 53: previous definition is here
# | 2 errors generated.
# `-----------------------------
# error: command failed with exit status: 1

--

```
</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/182707