[clang] [clang] Fix a crash when default argument is passed to an explicit object parameter (PR #177534)

[Corentin Jabot via cfe-commits]

cor3ntin wrote:

There seems to be test failures 

```
T06:40:53.4093969Z /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 -fsyntax-only -std=c++2b -Woverloaded-virtual /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/SemaCXX/cxx2b-deducing-this.cpp -verify
2026-01-31T06:40:53.4099000Z # 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 -fsyntax-only -std=c++2b -Woverloaded-virtual /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/SemaCXX/cxx2b-deducing-this.cpp -verify
2026-01-31T06:40:53.4101633Z # .---command stderr------------
2026-01-31T06:40:53.4102374Z # | error: 'expected-error' diagnostics seen but not expected: 
2026-01-31T06:40:53.4104074Z # |   File /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/SemaCXX/cxx2b-deducing-this.cpp Line 1470: expected '}'
2026-01-31T06:40:53.4105378Z # | error: 'expected-note' diagnostics seen but not expected: 
2026-01-31T06:40:53.4106730Z # |   File /home/gha/actions-runner/_work/llvm-project/llvm-project/clang/test/SemaCXX/cxx2b-deducing-this.cpp Line 1434: to match this '{'
2026-01-31T06:40:53.4107879Z # | 2 errors generated.
2026-01-31T06:40:53.4108277Z # `-----------------------------
2026-01-31T06:40:53.4108713Z # error: command failed with exit status: 1
2026-01-31T06:40:53.4109058Z 
2026-01-31T06:40:53.4109459Z --

```

https://github.com/llvm/llvm-project/pull/177534