[llvm] r262455 - Bug 20810: Use report_fatal_error instead of unreachable

[Matt Arsenault via llvm-commits]

> On Mar 1, 2016, at 20:30, David Blaikie via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Test cases?

These are essentially asserts. Every one of these would be a bug. This pass is very buggy and we don’t want to truly crash if these are hit.

-Matt