title: clang fails with pip install on macos
body: <p>I am running <code>pip install scrypt==0.8.0</code>.<br>
  I get the following error: <code>error: command '/usr/bin/clang' failed with exit status 1</code>.
  I have xcode-select, gcc etc. installed. when i try to <code>cd</code> into that folder it doesn't exist and running <code>clang --version</code> it gives me:</p>
  
  <pre><code>Apple LLVM version 9.0.0 (clang-900.0.38)
  Target: x86_64-apple-darwin17.2.0
  Thread model: posix
  InstalledDir: /Library/Developer/CommandLineTools/usr/bin
  </code></pre>
  
  <p>full error: <a href="https://pastebin.com/JZW1jRCy" rel="nofollow noreferrer">https://pastebin.com/JZW1jRCy</a></p>