[clang] [llvm] [clang][RISCV] Use macro to check if intrinsics are supported (PR #187197)

[Brandon Wu via cfe-commits]

4vtomat wrote:

> Probably misses a `REQUIRES` in test, I would think https://lab.llvm.org/buildbot/#/builders/10/builds/27817

oops, thanks!
fixed in this PR: https://github.com/llvm/llvm-project/pull/195605

https://github.com/llvm/llvm-project/pull/187197