Now that the command interpreter runs in a separate thread in Xcode, we need...

Now that the command interpreter runs in a separate thread in Xcode, we need to lock the target API lock instead of trying to lock it.

What was happening was:
1 - Xcode ran and stopped and was doing work on thread 2
2 - Users would type something in Xcode console on thread 1
3 - thread 3 would be running command interpreter thread and try to execute command but get "failed to get API lock" error for any command that wanted the target API lock (like "expression")

<rdar://problem/15775016>

llvm-svn: 200997