title: nullability-completeness warning since Xcode 9.3
body: <p><a href="http://clang.llvm.org/docs/DiagnosticsReference.html#wnullability-completeness" rel="nofollow noreferrer">The "nullability-completeness" warning</a> is not working in Xcode 9.3 (and 9.4.1) for me.
  It works though in Xcode 9.1 and 9.2.</p>
  
  <p>I created a new iOS project in Xcode 9.2 (or 9.1) with the "Single View App" template, then add this method to my ViewController.h:</p>
  
  <pre><code>- (nonnull UIView *)f:(UIView *)f g:(UIView *)g;
  </code></pre>
  
  <p>I'm getting 2 warnings on each of the arguments as expected like so:</p>
  
  <pre><code>In file included from /Users/daniel/Projects/tests/TestNullability92/TestNullability92/ViewController.m:9:
  /Users/daniel/Projects/tests/TestNullability92/TestNullability92/ViewController.h:13:31: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
  - (nonnull UIView *)f:(UIView *)f g:(UIView *)g;
                                ^
  /Users/daniel/Projects/tests/TestNullability92/TestNullability92/ViewController.h:13:31: note: insert '_Nullable' if the pointer may be null
  - (nonnull UIView *)f:(UIView *)f g:(UIView *)g;
                                ^
                                 _Nullable
  /Users/daniel/Projects/tests/TestNullability92/TestNullability92/ViewController.h:13:31: note: insert '_Nonnull' if the pointer should never be null
  - (nonnull UIView *)f:(UIView *)f g:(UIView *)g;
  </code></pre>
  
  <p>But if I open and rebuild that project in Xcode 9.3 (or 9.4.1) - I don't get those warnings.</p>
  
  <p>I tried going to the build settings and enabling this flag explicitly (although it should be enabled by default), but still got nothing:</p>
  
  <p><a href="https://i.stack.imgur.com/oGkUq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oGkUq.png" alt="enter image description here"></a></p>