Fix linking of drawing example

Commit 80e1340e introduced using a GDK method in examples/drawing.c, so
actually link that to GDK. Fixes build failure with --as-needed linker option
and gcc 4.5.

examples/Makefile.am

@@ -48,6 +48,9 @@ LDADD = \
 	$(top_builddir)/gtk/libgtk-3.0.la	\
 	$(GTK_DEP_LIBS)
 
+drawing_LDADD = $(LDADD) \
+	$(top_builddir)/gdk/libgdk-3.0.la
+
 noinst_PROGRAMS = \
 	hello-world				\
 	window-default				\