<rdar://problem/11400476>

On Lion, because the rights initially doesn't exist in /etc/authorization, if an admin user logs in and uses lldb within the first 5 minutes, it is possible to do AuthorizationCopyRights on LaunchUsingXPCRightName and get the rights back. As another security measure, we make sure that the LaunchUsingXPCRightName rights actually exists.

Removed Xcode as the user of the XPC service to shrink the security surface area.

llvm-svn: 156424