loader: Use dlsym to get our udev symbols instead of explicit linking.

loader: Use dlsym to get our udev symbols instead of explicit linking.

Steam links against libudev.so.0, while we're linking against
libudev.so.1.  The result is that the symbol names (which are the same in
the two libraries) end up conflicting, and some of the usage of .so.1
calls the .so.0 bits, which have different internal structures, and
segfaults happen.

By using a dlopen() with RTLD_LOCAL, we can explicitly look for the
symbols we want, while they get the symbols they want.

Reviewed-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Tested-by: Alexandre Demers <alexandre.f.demers@gmail.com>
Tested-by: Mike Lothian <mike@fireburn.co.uk>