libdbus-1.la: have proper dependencies on Windows

libdbus-1.la: have proper dependencies on Windows

Assigning to libdbus_1_la_DEPENDENCIES defeats Automake's normal
dependency logic, which makes libdbus-1.la depend on all the
static libraries that will go into it (it still had a corrct dependency
on the other objects, which go through a separate variable).
This meant libdbus-init-win wasn't necessarily built first.

Use EXTRA_libdbus_1_la_DEPENDENCIES to avoid that problem.

Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=68505
Acked-by: Ralf Habacker <ralf.habacker@freenet.de>