title: Build fails because of "lexical or preprocessor issue" relating to bits/os_defines.h
body: <p>When I try to build, I'm suddenly getting the error</p>
  
  <blockquote>
    <p>Lexical or Preprocessor Issue 'bits/os_defines.h' file not found</p>
  </blockquote>
  
  <p><img src="https://i.stack.imgur.com/r1rxj.png" alt=""></p>
  
  <p>What could possibly cause this?</p>
  
  <p><code>/usr/include/c++/4.2.1/bits</code> looks fine.</p>