[clang] [FMV][RISCV] Add __riscv_feature_bits.length check (PR #110098)

[Philip Reames via cfe-commits]

preames wrote:

Why?  There has only ever been one version of the features array, and that has not yet been published.  Why do we need a version check here at all?

https://github.com/llvm/llvm-project/pull/110098