Cannot build on windows with libusb

[JohnAZoidberg]

I tried to do it myself and then I noticed the GitHub action CI also can't do it:

-- Could NOT find LIBUSB (missing: LIBUSB_LIBRARIES LIBUSB_INCLUDE_DIR) 
libUSB is not found - no USB support will be built

In the run of "Build & Test (windows-latest, Ninja, mbedtls, libusb, compile)"

[lurch]

Well that's unexpected! @will-v-pi I guess the CI-test should check that in the libusb-included builds, the picotool help output lists the load command as being available?

[will-v-pi]

What version of libusb are you downloading, and did you definitely set the LIBUSB_ROOT environment variable, or pass -DLIBUSB_ROOT=/path/to/libusb to CMake?

I've just tested with the latest (https://github.com/libusb/libusb/releases/download/v1.0.29/libusb-1.0.29.7z) and it's working fine for me - the issue with the action was not setting the environment variable correctly, which I'm fixing now