Prevent client from querying each thread's PC at each stop.

Summary:
The server was no longer sending the thread PCs the way the client
expected them.
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
server.
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

llvm-svn: 292611
diff --git a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h
index 6423abc..1ecd582 100644
--- a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h
+++ b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h
@@ -417,6 +417,7 @@
   void HandleStopReply() override;
   void HandleAsyncStructuredDataPacket(llvm::StringRef data) override;
 
+  void SetThreadPc(const lldb::ThreadSP &thread_sp, uint64_t index);
   using ModuleCacheKey = std::pair<std::string, std::string>;
   // KeyInfo for the cached module spec DenseMap.
   // The invariant is that all real keys will have the file and architecture