[clang] [Clang] Fix handling of explicit parameters in `SemaLambda` (PR #168558)

[Willem Kaufmann via cfe-commits]

WillemKauf wrote:

`BuildAndTestWindows`:

```
   Failed Tests (1):
    SanitizerCommon-Unit :: ./Sanitizer-x86_64-Test.exe/StopTheWorld/SuspendThreadsAdvanced
```

https://github.com/llvm/llvm-project/pull/168558