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

[Piyou Chen via cfe-commits]

BeMg wrote:

The warning occurs because the RISC-V target_clones syntax `__attribute__((target_clones("default", "arch=+zba,+v,+c,+zicond", "arch=+zbb,+c,+v")))` contains a comma inside double quotes.

```
warning: mixing 'target_clones' specifier mechanisms is permitted for GCC compatibility; 
use a comma separated sequence of string literals, or a string literal containing a comma-separated list of versions
```

Should we suppress this warning for RISC-V target? Or change the target_clones syntax?

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