[clang] [X86][vectorcall] Do not consume register for indirect return value (PR #97939)

[Reid Kleckner via cfe-commits]

rnk wrote:

I lost the `__fastcall` or `__vectorcall` during editing, here's a fixed link: https://godbolt.org/z/46j33z8bc

You can see the load from [edx] and store to [ecx]:
```
NonTrivial copy_nontrivial(NonTrivial *) PROC   ; copy_nontrivial, COMDAT
        mov     eax, DWORD PTR [edx]
        mov     DWORD PTR [ecx], eax
...
```


https://github.com/llvm/llvm-project/pull/97939