Fix race condition in process resume

Summary:
Gdb-remote's async thread sent out the eBroadcastBitRunPacketSent message *before* actually
sending out the continue packet. Since it's this message the actually triggers the public state
transition, it could happen (and it did happen in TestAttachResume, which does an "process
interrupt" right after a continue) that we attempt to stop the inferior before it was actually
started (which obviously did not end well). This fixes the problem by moving the broadcast after
the packet was actually sent.

Reviewers: clayborg

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D14083

llvm-svn: 251399