[clang] [libcxxabi] [clang][ItaniumMangle] Mangle friend function templates with a constr… (PR #110247)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-gcc-ubuntu` running on `sie-linux-worker3` while building `clang,libcxxabi` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/174/builds/6025

<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 :: CodeGenCXX/mangle-concept.cpp' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
RUN: at line 1: /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/clang -cc1 -internal-isystem /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/lib/clang/20/include -nostdsysteminc -verify -std=c++20 -emit-llvm -triple x86_64-unknown-linux-gnu -o - /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp -fclang-abi-compat=latest | /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp
+ /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp
+ /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/clang -cc1 -internal-isystem /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/lib/clang/20/include -nostdsysteminc -verify -std=c++20 -emit-llvm -triple x86_64-unknown-linux-gnu -o - /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp -fclang-abi-compat=latest
error: 'expected-error' diagnostics seen but not expected: 
  File /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp Line 39: redefinition of 'h'
  File /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp Line 38: default template argument not permitted on a friend template
  File /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp Line 45: redefinition of 'j'
  File /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp Line 44: default template argument not permitted on a friend template
  File /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp Line 51: redefinition of 'l'
  File /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp Line 50: default template argument not permitted on a friend template
error: 'expected-note' diagnostics seen but not expected: 
  File /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp Line 55: in instantiation of template class 'test2::A<bool>' requested here
  File /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp Line 39: previous definition is here
  File /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp Line 45: previous definition is here
  File /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp Line 51: previous definition is here
10 errors generated.
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/clang/test/CodeGenCXX/mangle-concept.cpp

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/110247