added ick optimization flags; invoke ${CC}/${CXX}

A little bit of optimization from 'ick' greatly decreases the time/memory required to compile the intermediate C code.  @xyproto can confirm this.

This first commit is strictly an improvement, so it should be merged regardless of what you do with the later one(s).

As a separate commit, I modified your code to use the user's CC and CXX environment variables.  It's less clear whether or not this is an improvement, as it might cause moderate slowdown in a couple of places.  I personally prefer the version that uses environment variables rather than specific compilers, but it's up to you whether or not you merge this.