Identify generic Builtins for use with GCC and Clang/LLVM

Placeholder Jeremy Bennett
2023-08-25T03:43:42Z

The CORE-V builtin specification requires that where generic builtins exist, they should be reused for CORE-V, rather than defining custom builtins.

This issue is to track the set of builtins for which this is relevant. We can still keep CORE-V specific naming as a wrapper for these in the header.