build: define first week day in the build script

Calendar is not handling locale correctly, e.g. user’ set language to
English (en-us) and format to Norwegian (nb-no), but Calendar assumes
English format rather than Norwegian.

Calendar code was ready to use the correct format, just like Shell and
GtkCalendar. The issue was in the build script which was setting the
correct locale variable responsible to make that code work.

This patch fixes the build script.

https://bugzilla.gnome.org/show_bug.cgi?id=762428

src/gcal-utils.c

@@ -18,6 +18,8 @@
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include "config.h"
+
 #include "gcal-utils.h"
 #include "gcal-event-widget.h"
 #include "gcal-view.h"