[llvm] [RISCV] Add support for inline asm constraint vd (PR #111653)

[Sam Elliott via llvm-commits]

lenary wrote:

I think you've missed making the relevant clang changes to `RISCVTargetInfo::validateAsmConstraint` to support `vd`.

I don't understand why this constraint is needed but it's good to stay in line with GCC.

https://github.com/llvm/llvm-project/pull/111653