Add ccache support on linux and bsd

This adds ccache to the build process. The result is a drop in recompile times that is pretty dramatic - openssl drops from ~2 minutes on my MBP to 20 seconds, with similar results across the board. It's a transparent addition - install it, link it as gcc/g++, and go for it.

I didn't add support for any of the alternate platforms (solaris, smartos, etc) that I wasn't confident would work transparently.