[clang] [RISCV][FMV] Support target_clones (PR #85786)

[Piyou Chen via cfe-commits]

BeMg wrote:

Inside the resolver function, a function named `__riscv_ifunc_select` is used to ensure that all additional extension requirements are met. It is temporary interface until proposal be ratified.

```
bool __riscv_ifunc_select(char *FeatureStr);
```


https://github.com/llvm/llvm-project/pull/85786