Ensure broadway backend links when using as-needed linking

Error message at:
http://pkgsubmit.mageia.org/uploads/failure/cauldron/core/release/20130617185755.wally.valstar.6794/log/gtk+3.0-3.9.4-1.mga4/build.0.20130617185804.log

<ovitters> mclasen_:
http://svnweb.mageia.org/packages/cauldron/gtk%2B3.0/current/SOURCES/gtk%2B-3.9.4-linking.patch?revision=444164&view=markup
<ovitters> mclasen_: gtk doesn't seem to link properly on Mageia
(as-needed thing probably)
<mclasen_> sure, looks fine
<ovitters> can I commit this?
<mclasen_> yes, please commit

gdk/broadway/Makefile.am

@@ -72,6 +72,9 @@ libgdk_broadway_la_SOURCES =		\
 	gdkbroadway-server.h	\
 	gdkbroadway-server.c
 
+libgdk_broadway_la_LIBADD = \
+	-lrt
+
 broadwayd_SOURCES = \
 	broadway-protocol.h		\
 	broadwayd.c 			\