In https://github.com/riscv-non-isa/rvv-intrinsic-doc/pull/116, we
propose a new set of intrinsics for unmasked tail undisturbed
instructions. This patch is the implementation of the proposal.
This is a preparation work for these new C intrinsics. This patch only
adds LLVM IR intrinsics. There is no compile time or binary size
problem.
// Input: (undisturbed, pointer, vl) maybe better.