title: Eliciting an "unrecognized command line option" from gcc
body: <p>I'm using gcc 7.3. If I compile e.g., <code>int main(){ }</code> with
  <code>gcc main.c -Wno-foo</code>, the compilation succeeds and I get no error output.</p>
  
  <p>Changing the source to <code>int main(){ int a[-1]; /*uncompilable*/ }</code> while maintaining the build command gets me:</p>
  
  <pre><code>main.c: In function ‘main’:
  main.c:3:6: error: size of array ‘a’ is negative
    int a[-1];
        ^
  main.c: At top level:
  cc1: warning: unrecognized command line option ‘-Wno-foo’
  </code></pre>
  
  <p>Can I force the <code>unrecognized command line option ‘-Wno-foo’</code> warning/error message without introducing a compilation error into the source?</p>
  
  <p><code>-Wfoo</code> (without the <code>no-</code>) gets me a warning message right away, but I'd rather keep the <code>no-</code> in there. (This is for compiler feature testing, which I do as part of my build.)</p>