[clang] [clang][RISCV] Support `norelax` attribute for RISCV (PR #115981)

[Yangyu Chen via cfe-commits]

cyyself wrote:

> I disagree that this is a thing which should exist. It's solving the problem in the wrong place.

Since a clean solution needs GLIBC update, I think this can be a workaround now for some generated IFUNC resolvers, such as target_clones or target_versions.

https://github.com/llvm/llvm-project/pull/115981