Fixed the async packets (packets that need to be sent to the GDB server

while the inferior is running) to be fast. The previous code would always
cause the sender to timeout, yet still return success due to the way we
were waiting for a value (incorrect value) to change. Now the ProcessGDBRemote
plug-in has a public and private "is running" predicate. This allows things
that need to send async packets to interrupt and wait for the private "is running"
state to be flipped to false, and then resume quickly with no timeout. 

llvm-svn: 123903