Sometimes ninja decides to compile tests/interactive-panels/main.c,
which requires shell/resources.h, before shell/resources.h is generated.
The fix is to use 'sources' argument of declare_dependency to properly
declare the dependency on generated headers.
A fix for tests/datetime and panels/datetime is also included in the
commit to fix a similar problem.
Closes https://gitlab.gnome.org/GNOME/gnome-control-center/merge_requests/472
