Added support for attaching to a remote debug server with the new command:

(lldb) process connect <remote-url>

Currently when you specify a file with the file command it helps us to find
a process plug-in that is suitable for debugging. If you specify a file you
can rely upon this to find the correct debugger plug-in:

% lldb a.out
Current executable set to 'a.out' (x86_64).
(lldb) process connect connect://localhost:2345
...

If you don't specify a file, you will need to specify the plug-in name that
you wish to use:

% lldb
(lldb) process connect --plugin process.gdb-remote connect://localhost:2345

Other connection URL examples:

(lldb) process connect connect://localhost:2345
(lldb) process connect tcp://127.0.0.1
(lldb) process connect file:///dev/ttyS1

We are currently treating the "connect://host:port" as a way to do raw socket
connections. If there is a URL for this already, please let me know and we
will adopt it.

So now you can connect to a remote debug server with the ProcessGDBRemote
plug-in. After connection, it will ask for the pid info using the "qC" packet
and if it responds with a valid process ID, it will be equivalent to attaching.
If it response with an error or invalid process ID, the LLDB process will be
in a new state: eStateConnected. This allows us to then download a program or
specify the program to run (using the 'A' packet), or specify a process to
attach to (using the "vAttach" packets), or query info about the processes
that might be available.

llvm-svn: 124846