title: GHC anything results in "ld: library not found for -lgmp"
body: <p>I'm trying to compile haskell programs on my mac running OS X 10.10 Yosemite, but ghc fails every time with <em><strong>ld: library not found for -lgmp</strong></em>:</p>
  
  <pre><code>$ ghc foo.hs
  [1 of 1] Compiling Main             ( foo.hs, foo.o )
  Linking foo ...
  ld: library not found for -lgmp
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  </code></pre>
  
  <p>Help?</p>