title: std::variant<>::get() does not compile with Apple LLVM 10.0
body: <p>I'm playing with the C++17 std::variant type and tried to compile the <a href="https://en.cppreference.com/w/cpp/utility/variant/get" rel="noreferrer">cppreference example code</a> for <code>get()</code>:</p>
  
  <pre><code>#include &lt;variant&gt;
  #include &lt;string&gt;
  
  int main()
  {
      std::variant&lt;int, float&gt; v{12}, w;
      int i = std::get&lt;int&gt;(v);
      w = std::get&lt;int&gt;(v);
      w = std::get&lt;0&gt;(v); // same effect as the previous line
  
  //  std::get&lt;double&gt;(v); // error: no double in [int, float]
  //  std::get&lt;3&gt;(v);      // error: valid index values are 0 and 1
  
      try {
        std::get&lt;float&gt;(w); // w contains int, not float: will throw
      }
      catch (std::bad_variant_access&amp;) {}
  }
  </code></pre>
  
  <p>in XCode 10. My project is set to C++17, but I get compiler errors:</p>
  
  <blockquote>
    <p>Call to unavailable function 'get': introduced in macOS 10.14</p>
  </blockquote>
  
  <p>and</p>
  
  <blockquote>
    <p>'bad_variant_access' is unavailable: introduced in macOS 10.14</p>
  </blockquote>
  
  <p>which is surprising in 2 ways: it should compile if <code>std::variant</code> is supported and the hint about macOS 10.14 is weird, given that I'm on that version and it has nothing to do with the supported C++ dialect (and the project's deployment target is 10.14).</p>
  
  <p>Is this something I'm doing wrong or a bug in clang?</p>