title: gcc -print-multi-os-directory error on mac
body: <p>My mac version is Sierra. Xcode 8.0 </p>
  
  <p>gcc info</p>
  
  <p><code>Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
  Apple LLVM version 8.0.0 (clang-800.0.42.1)
  Target: x86_64-apple-darwin16.4.0
  Thread model: posix
  InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin</code></p>
  
  <p>I think gcc is not problem. My project build option is <code>-print-multi-os-directory</code>. but my gcc unsupported... what's the problem???</p>
  
  <p>thanks</p>