CMake improvement -- using pkg-find to find the libraries

[mcuee]

From the comment by @Youw here.

• macOS github action failed. #1793 (comment)

Yeap, this is the reason:

For libusb project, we usually recommend using pkg-config to find libusb.h and not to use libusb-1.0/libusb.h in any case.
https://github.com/avrdudes/avrdude/blob/main/src/avrftdi_private.h

It is not enough to install pkg-config. One must explicitly use it to find a package.

The propper way would be to remove things like find_library(HAVE_LIBUSB_1_0 ...) and similar nonsense with a propper use of cmake/pkg-config, e.g. in a similar way like HIDAPI does it.

[mcuee]

@ndim

In case you continue the work on the CMake improvement along with autotools improvement, maybe you want to take a look at the above recommendations. Thanks.

[ndim]

Now that the gpiod support requires pkg-config logic anyway, we can jump on board completely, both on the cmake and on the automake side.

Both for finding our own dependencies and for installing a libavrdude-2.pc alongside libavrdude.