Fix android build on Darwin.

This cleans up configure and Makefile.in so that things build correctly on Darwin.
auto merge of #826 : metajack/servo/android-darwin, r=jdm

This cleans up configure and Makefile.in so that things build correctly on Darwin.

This needs https://github.com/mozilla-servo/nss/pull/6 before it can be merged. Please hold any r+ until that lands and I push the submodule update.