I was thinking that this is when we should use GH_TAGNAME. However, the example from the Handbook you mentioned in the PR does the same. Hum!

I'd rather do this

if(CMAKE_SYSTEM_NAME STREQUAL FreeBSD)
  set(USB_LIBRARY usb-1.0)
else()
  set(USB_LIBRARY usb)
endif()

and the use ${USB_LIBRARY} in the target_link_libraries()call.

Ditto, probably? Do we really need to repeat the whole block of install() calls?

Another problem is that it installs into fixed prefix. I think you can just write DESTINATION etc/airsane it will work automagically.

I'm afraid, this should be done at post-patch with REINPLACE_CMD. This way we can substitute the real PREFIX value and not fix it to /usr/local.