[flext] Compiling libs statically into an external

[Spencer Russell]

I've got an external that uses libusb, and so far it's working great
on Linux with PD and OSX with Max/MSP. As I'm starting to think about
distribution it would be great if it was just a single external that I
could distribute, especially for the OSX users who don't have as
convenient a way to install shared libs.

What would be the best way to get the flext build system to link
libusb statically into my external?

Thanks,
Spencer