Revert r176154 in favor of a better approach.

Code generation makes some basic assumptions about the IR it's been given. In
particular, if there is only one 'invoke' in the function, then that invoke
won't be going away. However, with the advent of the `llvm.donothing' intrinsic,
those invokes may go away. If all of them go away, the landing pad no longer has
any users. This confuses the back-end, which asserts.

This happens with SjLj exceptions, because that's the model that modifies the IR
based on there being invokes, etc. in the function.

Remove any invokes of `llvm.donothing' during SjLj EH preparation. This will
give us a CFG that the back-end won't be confused about. If all of the invokes
in a function are removed, then the SjLj EH prepare pass won't insert the bogus
code the relies upon the invokes being there.
<rdar://problem/13228754&13316637>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176677 91177308-0d34-0410-b5e6-96231b3b80d8
Couple of test fixes for r176671.

Not sure why these aren't failing on my linux machine, but this should cover
it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176678 91177308-0d34-0410-b5e6-96231b3b80d8
Another test fix for r176671.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176679 91177308-0d34-0410-b5e6-96231b3b80d8