build: Fix srcdir != builddir with wayland-client-protocol.h

In the gnome-ostree model builddir contains all generated files not in
git (unless the build system explicitly overrides that).  Here the
wayland-client-protocol.h was in $(builddir)/wayland, so we need to
find it using our already extant -I$(top_builddir)/gdk, rather than
relying on same-directory lookup.
gtkwidget: Fix issues with baseline alignment comparison
accessible: Fix test runner

This was an obvious typo.
gdkframeclockidle: Add explicit fallthrough markers

So people reading the code don't get confused.
Update French translation