[clang] [clang] CTAD alias: Emit a more descriptive diagnostic message when is_deducible constraint is evaluated to false. (PR #92389)

[via cfe-commits]

zeroomega wrote:

Hi @hokein , your change probably broke the test "Clang :: SemaCXX/cxx20-ctad-type-alias.cpp" on Windows. Could you take a look please?

We are seeing test failures on this with error message:

```
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
c:\b\s\w\ir\x\w\llvm_build\bin\clang.exe -cc1 -internal-isystem C:\b\s\w\ir\x\w\llvm_build\lib\clang\19\include -nostdsysteminc -fsyntax-only -Wno-c++11-narrowing -Wno-literal-conversion -std=c++20 -verify C:\b\s\w\ir\x\w\llvm-llvm-project\clang\test\SemaCXX\cxx20-ctad-type-alias.cpp
# executed command: 'c:\b\s\w\ir\x\w\llvm_build\bin\clang.exe' -cc1 -internal-isystem 'C:\b\s\w\ir\x\w\llvm_build\lib\clang\19\include' -nostdsysteminc -fsyntax-only -Wno-c++11-narrowing -Wno-literal-conversion -std=c++20 -verify 'C:\b\s\w\ir\x\w\llvm-llvm-project\clang\test\SemaCXX\cxx20-ctad-type-alias.cpp'
# .---command stderr------------
# | error: 'expected-note' diagnostics expected but not seen: 
# |   File C:\b\s\w\ir\x\w\llvm-llvm-project\clang\test\SemaCXX\cxx20-ctad-type-alias.cpp Line 112: cannot deduce template arguments for 'Bar' from 'Foo<int, 4UL>'
# | error: 'expected-note' diagnostics seen but not expected: 
# |   File C:\b\s\w\ir\x\w\llvm-llvm-project\clang\test\SemaCXX\cxx20-ctad-type-alias.cpp Line 112: cannot deduce template arguments for 'Bar' from 'Foo<int, 4ULL>'
# | 2 errors generated.
# `-----------------------------
# error: command failed with exit status: 1

--
```

This happens on our Windows builder. Link to the task: https://ci.chromium.org/ui/p/fuchsia/builders/toolchain.ci/clang-windows-x64/b8747755569988931969/overview

https://github.com/llvm/llvm-project/pull/92389