title: Why xcode-select: error :command line tools are already installed, use "Software Update" to install updates
body: <p>i wanted to:   brew install macvim --override-system-vim
  meet a problems:</p>
  
  <blockquote>
    <p>macvim: A full installation of Xcode.app is required to compile this   software.
    Installing just the Command Line Tools is not sufficient.
    Installing just the Command Line Tools is not sufficient.
    Xcode can be installed from the App Store.
    <code>Error: An unsatisfied requirement failed this build.</code></p>
  </blockquote>