We require OS X SDK 10.8 or newer now

Change-Id: I68eee76c8710c89af8e3c1e1006345f908923ece
We always build 64-bit OS X code

Change-Id: I527c66c7be1372ab5ddf86625667d2f315e9b5d3
Bin leftover stray variable assignment

Change-Id: I75baf1f8b49e05702528af72b2f364a9b152d50c