Patch: Exception Handling in libobjc2 with latest clang builds

[Mathias Bauer]

Hi dear list,

as already reported here, the exception handling in libobjc2 does not 
work correctly on ARM platforms. The personality routine misses the 
virtual stack unwinding required by the ARM EHABI spec.

I asked Logan Chien, who was involved in getting the ARM EHABHI stuff 
into llvm, for help and he sent me a patch that solved the problem.

The patch makes the ExceptionTest.m work on the ARM systems he and I 
tested it on. The test cases for C++ and foreign exceptions still don't 
work, buth there are other reasons for that (e.g. that the code that 
there is no code that handles C++ exceptions on ARM).

So first of all: many thanks to Logan!

He asked me to post the patch here, so that's what I do now. Please give 
it a review.