Prevent client from querying each thread's PC at each stop.
The server was no longer sending the thread PCs the way the client
I changed the server to send them back as a threadstop info field,
similar to the Apple version of the server.
I also changed the client to look for them there, before querying the
I added a test to ensure the server doesn't stop sending them.
Reviewed By: labath
Differential Revision: https://reviews.llvm.org/D28880
Author: Jason Majors