Changes to lldb and debugserver to reduce extraneous memory reads

at each public stop to improve performance a bit.  Most of the 
information lldb needed was already in the jThreadsInfo response;
complete that information and catch a few cases where we could still
fall back to getting the information via discrete memory reads.


debugserver adds 'associated_with_dispatch_queue' and 'dispatch_queue_t
keys to the jThreadsInfo response for all the threads.  lldb needs the
dispatch_queue_t value.  And associated_with_dispatch_queue helps to
identify which threads definitively don't have any queue information so
lldb doesn't try to do memory reads to get that information just because
it was absent in the jThreadsInfo response.

Remove the queue information from the questionmark (T) packet.  We'll
get the information for all threads via the jThreadsInfo response -
sending the information for the stopping thread (on all the private
stops, plus the less frequent public stop) was unnecessary information
being sent over the wire.

SystemRuntimeMacOSX will try to get information about queues by asking
the Threads for them, instead of reading memory.  

ProcessGDBRemote changes to recognize the new keys being sent in the
jThreadsInfo response.  Changes to ThreadGDBRemote to track the new
information.  Also, when a thread is marked as definitively not 
associated with a libdispatch queue, don't fall back to the system
runtime to try memory reads to find the queue name / kind / ID etc.


<rdar://problem/23309359> 

llvm-svn: 257453