examples: Move $(WARN_CFLAGS) to $(AM_CFLAGS)

$(AM_CPPFLAGS) is for passing options to the C preprocessor,
not the C compiler, and the stuff in $(WARN_CFLAGS) belongs
to the latter category.
Signed-off-by: NAndrea Bolognani <abologna@redhat.com>
Acked-by: NMichal Privoznik <mprivozn@redhat.com>

examples/Makefile.am

@@ -29,6 +29,9 @@ EXTRA_DIST = \
 AM_CPPFLAGS = \
 	-I$(top_builddir)/include \
 	-I$(top_srcdir)/include \
+	$(NULL)
+
+AM_CFLAGS = \
 	$(WARN_CFLAGS) \
 	$(NULL)