[clang] [clang] Prevent recursive copy initialization during variadic argument promotion (PR #196744)

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github-actions[bot] wrote:

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

* 53878 tests passed
* 1202 tests skipped
* 1 test failed

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

### Clang
<details>
<summary>Clang.CXX/drs/cwg6xx.cpp</summary>

```
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
c:\_work\llvm-project\llvm-project\build\bin\clang.exe -cc1 -internal-isystem C:\_work\llvm-project\llvm-project\build\lib\clang\23\include -nostdsysteminc -std=c++98 C:\_work\llvm-project\llvm-project\clang\test\CXX\drs\cwg6xx.cpp -fexceptions -fcxx-exceptions -pedantic-errors -verify-directives -verify=expected,cxx98-17,cxx98-14,cxx98
# executed command: 'c:\_work\llvm-project\llvm-project\build\bin\clang.exe' -cc1 -internal-isystem 'C:\_work\llvm-project\llvm-project\build\lib\clang\23\include' -nostdsysteminc -std=c++98 'C:\_work\llvm-project\llvm-project\clang\test\CXX\drs\cwg6xx.cpp' -fexceptions -fcxx-exceptions -pedantic-errors -verify-directives -verify=expected,cxx98-17,cxx98-14,cxx98
# .---command stderr------------
# | error: diagnostics with 'error' severity expected but not seen: 
# |   File C:\_work\llvm-project\llvm-project\clang\test\CXX\drs\cwg6xx.cpp Line 756 (directive at C:\_work\llvm-project\llvm-project\clang\test\CXX\drs\cwg6xx.cpp:760) 'expected-error': no matching constructor for initialization of 'volatile Y'
# | error: diagnostics with 'error' severity seen but not expected: 
# |   File C:\_work\llvm-project\llvm-project\clang\test\CXX\drs\cwg6xx.cpp Line 756: cannot pass object of non-POD type 'volatile Y' through variadic function; call will abort at runtime
# | error: diagnostics with 'note' severity expected but not seen: 
# |   File C:\_work\llvm-project\llvm-project\clang\test\CXX\drs\cwg6xx.cpp Line 732 (directive at C:\_work\llvm-project\llvm-project\clang\test\CXX\drs\cwg6xx.cpp:761) 'expected-note': candidate constructor (the implicit copy constructor) not viable: 1st argument ('volatile Y') would lose volatile qualifier
# |   File C:\_work\llvm-project\llvm-project\clang\test\CXX\drs\cwg6xx.cpp Line 732 (directive at C:\_work\llvm-project\llvm-project\clang\test\CXX\drs\cwg6xx.cpp:762) 'expected-note': candidate constructor (the implicit default constructor) not viable: requires 0 arguments, but 1 was provided
# | 4 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/196744