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
```
The application module `app` serves double duties of providing the prebuilt Godot binaries ('android_debug.apk', 'android_release.apk') and the Godot custom build template ('android_source.zip').
As of clang-format 6.0.1, putting the `/* clang-format off */` hint
around our "invalid" `[vertex]` and `[shader]` statements isn't enough
to prevent a bogus indent of the next comments and first valid statement,
so we need to enclose that first valid statement in the unformatted chunk.
