title: stdlibc++ headers not found error on xcode 10
body: <p>We have some c libraries written for our iOS project and after upgrading to Xcode 10, when compiling we get the error:</p>
  
  <pre><code>error: include path for stdlibc++ headers not found; pass ‘-std=libc++’
  on the command line to use the libc++ standard library instead
  [-Werror,-Wstdlibcxx-not-found]
          1 error generated.
  </code></pre>
  
  <p>Where do we need to make changes in out makefiles? Because I don't find the '-std='argument in them.</p>