There seem to be a "port" of GNU/Linux's libevdev on FreeBSD.
However, it's not exactly a port, and it includes linux/input.h
file which on FreeBSD doesn't exist. The equivalent file for
linux/input.h is dev/evdev/input.h.
Unless the upstream maintainer of libevdev adds this (may not), we
should add a note here, describing the possible error on compilation
of 86Box on FreeBSD.
Without this, the build fails with:
```
Make Error at /usr/lib64/cmake/ZLIB/ZLIB.cmake:81 (message):
The imported target "ZLIB::zlibstatic" references the file
"/usr/lib64/libz.a"
but this file does not exist. Possible reasons include:
* The file was deleted, renamed, or moved to another location.
* An install or uninstall procedure did not complete successfully.
* The installation package was faulty and contained
"/usr/lib64/cmake/ZLIB/ZLIB.cmake"
but not all the files it references.
Call Stack (most recent call first):
/usr/lib64/cmake/ZLIB/zlib-config.cmake:44 (include)
/usr/share/cmake/Modules/FindPNG.cmake:65 (find_package)
src/CMakeLists.txt:136 (find_package)
```
* Add FluidSynth and libslirp to dependencies where they haven't been added already
* Remove FAudio from installation commands, but still mention it as an alternative to OpenAL
* Replace pkg-config with pkgconf for MSYS2 and Arch
* Drop the multilib OpenAL requirement on Arch
