deps: fix gyp to work on MacOSX without XCode

This is a port of eb459c81 ,
used as a floating patch over gyp.

Original commit message:

  This issue has already submitted to the upstream in
  https://code.google.com/p/gyp/issues/detail?id=477
  Use this commit until the upstream is to be fixed.

  PR-URL: https://github.com/iojs/io.js/pull/1325


Reviewed-By: Fedor Indutny <fedor@indutny.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

This was ported to v0.10 in https://github.com/joyent/node/pull/25857

PR-URL: https://github.com/nodejs/node/pull/2843


Reviewed-By: rvagg - Rod Vagg <rod@vagg.org>
Reviewed-By: orangemocha - Alexis Campailla <orangemocha@nodejs.org>
Reviewed-By: bnoordhuis - Ben Noordhuis <info@bnoordhuis.nl>