Merge commit 7214f7a79 from llvm git (by Sam Elliott):

[brooks]

Summary

[RISCV] Lower llvm.trap and llvm.debugtrap

Summary:
Until this commit, these have lowered to a call to abort().

`llvm.trap()` now lowers to `unimp`, which should trap on all systems.

`llvm.debugtrap()` now lowers to `ebreak`, which is exactly what this
instruction is for.

Reviewers: asb, luismarques

Reviewed By: asb

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69390

This fixes miscompilation resulting in linking failures with
INVARIANTS disabled.

[brooks]

This change is required to add a working GENERIC-NODEBUG kernel.

[dim]

LGTM