[RFC]xf86-input-evdev: use libsysdev as build-time fallback if libudev is missing

[Isaac Dunham]

Hello,
Having grown tired of hearing complaints about udev dependencies, I
wrote a library that does a very small subset of what libudev does with
a slightly more concise API. It does not care how /dev is managed.
The code may be found at:
github.com/idunham/libsysdev.git

I have ported xf86-input-evdev to use said library; the attached
patch will allow building with it as a compile-time fallback.
Does anyone have comments on this patch?

I'm aware that it would be possible to share much of the code by using
more #ifdef USE_UDEV; if that is better, I can adjust this.

Please note: I am *not* interested in arguing about udev, whether pro
or con. I'm just asking for a review of this patch.

Thanks,
Isaac Dunham