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

[Piyou Chen via cfe-commits]

BeMg wrote:

The proposal can be found at the https://github.com/riscv-non-isa/riscv-c-api-doc/pull/48.

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