[llvm] fix preserve_none in X86 backend (PR #192300)

[via llvm-commits]

weiguozhi wrote:

At the end of CC_X86_64_Preserve_None we have
```
  ...
  // Otherwise it's the same as the regular C calling convention.
  CCDelegateTo<CC_X86_64_C>
```
So I expect everything not specified in CC_X86_64_Preserve_None should be delegated to CC_X86_64_C, including ```CCIfByVal<CCPassByVal<8, 8>>```,  but why doesn't it work in this case?


https://github.com/llvm/llvm-project/pull/192300