scanner: Improve XML parse error reporting
scanner: Improve XML parse error reporting

Print the parse error and exit with a failure if expat can't parse the
XML.

Signed-off-by: Jonas Ådahl <67dcd8a17e758192e0cbb577ce1d62cc7da6cf49@gmail.com>

tulcod/wayland,tulcod/wayland,sir-murray/wayland,abooij/wayland,bitfactor/wayland,mchalupa/wayland,mchalupa/wayland,bitfactor/wayland,eyolfson/wayland,sir-murray/wayland,eyolfson/wayland,abooij/wayland,sir-murray/wayland,bitfactor/wayland,tulcod/wayland,eyolfson/wayland,abooij/wayland,mchalupa/wayland