Fix segfault notification in lldb-mi

Summary:
This patch adds system exception handling in lldb-mi + tests.

All tests pass on OS X.

Reviewers: zturner, abidh, clayborg

Reviewed By: clayborg

Subscribers: emaste, lldb-commits, zturner, clayborg, abidh

Differential Revision: http://reviews.llvm.org/D7500

llvm-svn: 228803