r177329 - This code works around what appears to be a bug in another part of clang.

[Rafael Espíndola]

> This code works around what appears to be a bug in another part of clang.
> I have filed http://llvm.org/bugs/show_bug.cgi?id=15538 against clang.
> This code is safer anyway because "cast" assumes you really know that
> it's okay to make the cast. In this case isa should not be false and
> dyn_cast should not return null as far as I understand. But everything
> else is valid so I did not want to revert my previous patch for attributes
> mips16/nomips16 or use an llvm_unreachable here which would make a number
> of our tests fail for mips.

I don't think this is a reasonable change. If there is a bug somewhere
else, it should be fixed. This change just hides it. It doesn't even
include a testcase. Please revert. If some other patch caused problem,
revert it too.

Cheers,
Rafael