I was having some serious issues getting my AII-SPI-USB command line tool (for transferring disk images to the UM232H) working on my newer MacBook. I tried rebuilding it, then rebuilding libftdi, and libusb, and libmpsse. I finally got things working and Xcode asked me to update my build settings. Then, of course, nothing would work again. The primary problem was "duplicate symbol" errors that were suddenly popping up. Some edits to libmpsse, and some changes to my code, and I finally was able to re-build it. I think I should staticly link the libraries I need for the tool, since most users won't have the will power to compile libftdi, or libusb to use it.
I need a new name for the program too. AII-SPI-USB is not a very posixy name for a command line tool. Maybe a2usbdsk.
It's ironic that one of the benefits of programming for retro computers is that the hardware or operating systems almost never change. Do it once, and it works forever! Not so for modern hardware, even the modern hardware interacting with the retro computer.