More lldb-platform for remote-linux support.

More work on https://github.com/tfiala/lldb/issues/32.

remote-linux now properly tries to start lldb-gdbserver.
lldb-gdbserver "helper binary app" Host support now does something
reasonable for Linux/FreeBSD/NetBSD.  It lops off the /lib dir for
the shared library, and replaces it with /bin if found, which will
be the case for linkage to liblldb.so.  For static linking, I need
to verify that this still works.

This now takes an lldb attached via lldb-platform up to the point
of trying to launch lldb-gdbserver.  Something about the args is
appearing to be wrong, need to diagnose.

This command sequence is what I use on the lldb side to talk to it:
$ /path/to/lldb -- /path/to/inferior/exe/loops
(lldb) log enable lldb platform
(lldb) platform select remote-linux
main-thread PlatformLinux::CreateInstance(force=true, arch={<null>,<null>})
main-thread PlatformLinux::CreateInstance() creating remote-linux platform
  Platform: remote-linux
 Connected: no
    Kernel: Linux
   Release: 3.13.0-30-generic
   Version: #54-Ubuntu SMP Mon Jun 9 22:45:01 UTC 2014
(lldb) platform connect connect://localhost:2000
main-thread PlatformRemoteGDBServer::GetRemoteWorkingDirectory() -> '/tmp/llpl'
  Platform: remote-linux
    Triple: x86_64--linux-gnu
OS Version: 3.13.0
  Hostname: tfiala2.mtv.corp.google.com
 Connected: yes
WorkingDir: /tmp/llpl
    Kernel: Linux
   Release: 3.13.0-30-generic
   Version: #54-Ubuntu SMP Mon Jun 9 22:45:01 UTC 2014
(lldb) file loops
Current executable set to 'loops' (x86_64).
(lldb) b main.cpp:10
Breakpoint 1: where = loops`main + 71 at main.cpp:10, address = 0x0000000000400657
(lldb) run
main-thread PlatformLinux::LaunchProcess() attempting to launch remote process
main-thread PlatformRemoteGDBServer::LaunchProcess() called
main-thread PlatformRemoteGDBServer::LaunchProcess() set launch architecture triple to 'x86_64-unknown-linux'
main-thread PlatformRemoteGDBServer::LaunchProcess() pid 13649 launched successfully
error: unable to launch a GDB server on 'tfiala2.mtv.corp.google.com'
(lldb)

The lldb-platform log looks like this:
1404343701.685592000 <  54> read packet: $qLaunchGDBServer;host:tfiala2.mtv.corp.google.com;#a0
1404343701.685624000 GDBRemoteCommunicationServer::Handle_qLaunchGDBServer() called
1404343701.685652000 Launching debugserver with: tfiala2.mtv.corp.google.com:0...

1404343701.685666000 GDBRemoteCommunication::StartDebugserverProcess(hostname=tfiala2.mtv.corp.google.com, in_port=0, out_port=0
1404343701.685700000 Host::GetLLDBPath() attempting to derive the bin path (ePathTypeSupportExecutableDir) from this path: /mnt/ssd/work/macosx.sync/mp-git/build-debug/lib
1404343701.685717000 Host::GetLLDBPath() derived the bin path as: /mnt/ssd/work/macosx.sync/mp-git/build-debug/bin
1404343701.685790000 Host::GetLLDBPath(ePathTypeSupportExecutableDir) => '/mnt/ssd/work/macosx.sync/mp-git/build-debug/bin'
1404343701.685827000 GDBRemoteCommunication::StartDebugserverProcess() found gdb-remote stub exe '/mnt/ssd/work/macosx.sync/mp-git/build-debug/bin/lldb-gdbserver'
1404343701.685972000 ::posix_spawnattr_init ( &attr ) err = 0x00000000
1404343701.685989000 ::posix_spawnattr_setflags ( &attr, flags=0x0000000c ) err = 0x00000000