Patches for Yosemite

This gets rippled going on Yosemite.

After upgrading you have to re-install command-line tools prior to building:
$ xcode-select --install

Tested on both Mavericks and Yosemite.  Passes Travis.
@josh-ripple @niq
In the C++ standard this is 16.3.5 [cpp.scope]/p2:
... It is ignored if the specified identifier is not currently defined as a macro name.