[clang] [llvm] [RISCV][MC] Introduce XSfvfexp* and XSfvfbfexpa* extensions and their MC supports (PR #164349)

[Jim Lin via llvm-commits]

https://github.com/tclin914 commented:

Should we also add tests for pre-defined macro in `clang/test/Preprocessor/riscv-target-features-sifive.c`

https://github.com/llvm/llvm-project/pull/164349