Enable listening for EXC_RESOURCE events, and format mach

event as a thread stop reason if we receive one, using 
some macros to decode the payload.  

Patch originally written by Fred Riss, with a few small changes
by myself.

Writing a test for this is a little tricky because the 
mach exception data interpretation relies on header macros
or function calls - it may change over time and writing
a gdb_remote_client test for this would break as older 
encoding interpretation is changed.  I'll tak with Fred
about this more, but neither of us has been thrilled with
the kind of tests we could write for it.

<rdar://problem/13097323>, <rdar://problem/40144456> 

llvm-svn: 346571