Enable TestExitDuringBreak.test_with_dwarf on Linux.

This test passed 50 out of 50 times for me on Unbuntu 12.04 LTS x86_64
with lldb built using gcc 4.8.2 and July 2013 libedit.

This is related to:
http://llvm.org/bugs/show_bug.cgi?id=16170