Pass input/output files as arguments to wayland-scanner

When input/output files are passed as arguments to wayland-scanner,
instead of using stdin/stdout, warning and error messages will contain
the file name, together with line number, of the warning/error. Doing
this helps IDEs jump to the correct line.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
[Pekka: dropped the src/scanner.mk hunk, file deleted]
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>