Revert the change to switch to the XCBuild system for a bit.
Revert the change to switch to the XCBuild system for a bit.

<rdar://problem/38693902>
<rdar://problem/38817254>

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb