Expose SBPlatform through the public API.

Example code:

remote_platform = lldb.SBPlatform("remote-macosx"); 
remote_platform.SetWorkingDirectory("/private/tmp")
debugger.SetSelectedPlatform(remote_platform)

connect_options = lldb.SBPlatformConnectOptions("connect://localhost:1111"); 
err = remote_platform.ConnectRemote(connect_options)
if err.Success():
    print >> result, 'Connected to remote platform:'
    print >> result, 'hostname: %s' % (remote_platform.GetHostname())
    src = lldb.SBFileSpec("/Applications/Xcode.app/Contents/SharedFrameworks/LLDB.framework", False)
    dst = lldb.SBFileSpec()
    # copy src to platform working directory since "dst" is empty
    err = remote_platform.Install(src, dst);
    if err.Success():
        print >> result, '%s installed successfully' % (src)
    else:
        print >> result, 'error: failed to install "%s": %s' % (src, err)


Implemented many calls needed in lldb-platform to be able to install a directory that contains symlinks, file and directories.

The remote lldb-platform can now launch GDB servers on the remote system so that remote debugging can be spawned through the remote platform when connected to a remote platform.

The API in SBPlatform is subject to change and will be getting many new functions.

llvm-svn: 195273