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

[Philip Reames via cfe-commits]

https://github.com/preames approved this pull request.

LGTM

(I only did a quick pass on this version assuming mostly unchanged from prior.  Wanted to explicitly chime in with support for the priority syntax.)

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