[clang] [llvm] [RISCV] Add MC layer support for XSfmm*. (PR #133031)

[Jiongjia Lu via cfe-commits]

Avimitin wrote:

> Is the issue really related to this PR? Why would a MC change cause CodeGen errors? Is it because uncommon extension combinations?

I've try to change march combination but which doesn't seems like the root cause of this issue. Even `-march=rv32gc_zve32f_xsfmm128t` could fail. But during the debug process I found that the root cause of this issue is from the `-O3` flag. The pass error could also happen for `-O2` flag. If I turn optimization flag off, or with `-O1`, `-O0`(the default optimization), `-Og`, the above problematic code could be compile successfully.

https://github.com/llvm/llvm-project/pull/133031