[Clang] Compiling and linking with `-gdwarf` generates PDB on Windows

When using `-gdwarf` Windows and linking with clang, a PDB file will be generated, because the linker is invoked with `-debug`. The PDB will only contain the `S_PUB32` entries for the symbols from the object files (plus records from the PDBs of the default libraries), but it's confusing that this is generated when DWARF debug info is requested.

To reproduce:
```console
> echo "int main(void){}" > test.c
> clang test.c -gdwarf -fuse-ld=lld -v
clang version 21.1.2
Target: x86_64-pc-windows-msvc
Thread model: posix
[...]
"C:\\Users\\johannes\\scoop\\apps\\llvm-full\\21.1.2\\bin\\lld-link" -out:a.exe -defaultlib:libcmt -defaultlib:oldnames -libpath:[...] -nologo -debug "C:\\Users\\johannes\\AppData\\Local\\Temp\\test-0a0970.o"
```

The flag is added here:
https://github.com/llvm/llvm-project/blob/7b98280b6b7cb89b141a5874ff9ee3ce72dab92a/clang/lib/Driver/ToolChains/MSVC.cpp#L167-L168

Is this expected/intentional?

Reproduce the Windows case with clang test.c -gdwarf -fuse-ld=lld -v and inspect clang/lib/Driver/ToolChains/MSVC.cpp at the linked lines where -debug is added. Determine the intended interaction between -gdwarf and linker PDB generation; done means the behavior is resolved and covered by an appropriate regression test.

Written by the indexing model from the issue text.