This makes it possibly to run Linux binaries compiled with udev support on
Linux systems which do not provide udev (typically systemd-less distros).
If udev is missing, we fall back to parsing `/dev/input` like when compiled
without udev support (`udev=no`).
Also adding some verbose debug statements to know which method we're using
when debugging Linux joypad issues.
The libudev so wrappers were generated on Mageia 8 with libudev 246.9 using
https://github.com/hpvb/dynload-wrapper:
```
./generate-wrapper.py --include /usr/include/libudev.h --sys-include '<libudev.h>' \
--soname libudev.so.1 --init-name libudev --omit-prefix gnu_ \
--output-header libudev-so_wrap.h --output-implementation libudev-so_wrap.c
```
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