Improve, refactor and clean up `tools/osx/builder` to build a relatively
full-featured ffmpeg as well. This requires lots of other dists. It's
kind of like a mini port system now. Will generalize it shortly to a
sourced library for using with both the mac and the mingw builds. Will
hopefully become a separate repo on github at some point.

Add perl dist support to the builder.

Add an `--env` flag to the builder to print the build environment
variables so that they can be read in with `eval` for debugging
purposes.

Also add the `FFMPEG_STATIC` cmake option to link static ffmpeg
libraries correctly.

Move the codesigning and zipping of the `.app` bundle to the builder
script and out of cmake, as this is something most users don't need.