Some more correctness fixes and code-size optimizations for fragile-ABI

ObjC exceptions:
  - don't enter a try for the catch blocks unless there's a finally
  - put the setjmp buffer in the locals set for liveness reasons
  - dump the sync object into an alloca in the locals set for liveness reasons
Some of this can go away if the backend starts to properly calculate liveness
in the presence of setjmp (which would also be a *much* stabler solution).

llvm-svn: 110188