Update to compile on FreeBSD.

[DanielO]

What it says on the tin, I have only tested on FreeBSD and only run a quick orbtop

[ALTracer]

Suggested change

	#include <libusb-1.0/libusb.h>
	#include <libusb.h>

Consider dropping the subfolder -- it is not needed, if Makefile + pkg-config, or meson, is used as the build system. This allows simplifying most of nested macros dispatch in here and other places. I tested building on Linux. Git annotate points to early Makefile from 2017 without pkg-config, where it could be attributed to pointing under /usr/include ad-hoc.

[ALTracer]

Confirming builds-and-runs successfully under NomadBSD 13.2-RELEASE -- it opens an swlink BMP-compatible's trace capture port, and the other tools launch. I did not have an appropriate ELF firmware file on that LiveUSB, so I did not test actual operation either.
The macro dispatch nest (which you're touching with this PR) could use some simplification, but being myself an external user/contributor, I can't ask you that.

[DanielO]

Yeah I didn't want to touch that too much, I wasn't sure why it was like it is.

You can detect Windows/FreeBSD/Linux/macOS/etc with pre-existing compiler defines so I am not sure why there is a Meson rule to add a define.

I'm also not sure why ioctl is declared manually on Linux etc.. I would expect the same includes that work on FreeBSD would work on Linux, but presumably they were added for a good reason.