title: `brew upgrade` hangs on El Capitan
body: <p>I can't run <code>brew upgrade</code> without it hanging indefinitely. I'm using El Capitan OS. Here's the input/output: </p>
  
  <pre><code>&gt;&gt;$ brew upgrade
  Updating Homebrew...
  ==&gt; Auto-updated Homebrew!
  Updated 2 taps (homebrew/core, homebrew/science).
  ==&gt; Updated Formulae
  artifactory         dovecot             node@4              scamper
  chromedriver        node-build          openvpn
  ==&gt; Deleted Formulae
  pdksh
  
  ==&gt; Upgrading 10 outdated packages, with result:
  gcc 6.2.0, gdbm 1.12, libtiff 4.0.7, openssl 1.0.2j, pkg-config 0.29.1_2, python 2.7.12_2, homebrew/science/r 3.3.2, readline 7.0.1, sqlite 3.15.2, yara 3.5.0_1
  ==&gt; Upgrading gcc
  Warning: Building gcc from source:
    The bottle needs the Xcode CLT to be installed.
  ==&gt; Using the sandbox
  ==&gt; Downloading https://ftpmirror.gnu.org/gcc/gcc-6.2.0/gcc-6.2.0.tar.bz2
  Already downloaded: /Users/r8t/Library/Caches/Homebrew/gcc-6.2.0.tar.bz2
  ==&gt; Downloading https://raw.githubusercontent.com/Homebrew/formula-patches/e9e0e
  Already downloaded: /Users/r8t/Library/Caches/Homebrew/gcc--patch-863957f90a934ee8f89707980473769cff47ca0663c3906992da6afb242fb220.patch
  ==&gt; Patching
  ==&gt; Applying 6.1.0-jit.patch
  patching file gcc/jit/Make-lang.in
  ==&gt; ../configure --build=x86_64-apple-darwin15.6.0 --prefix=/usr/local/Cellar/gc
  ==&gt; make bootstrap
  </code></pre>
  
  <p>And then nothing. </p>