Fix linking xine_artsplugin with pthread

Thanks to Francois Andriot
(legacy RedHat patch)
(cherry picked from commit 1973b023a9)

xine_artsplugin/Makefile.am

@@ -8,7 +8,7 @@ libarts_xine_la_SOURCES = xinePlayObject.cc \
 			  xinePlayObject_impl.cpp \
 			  audio_fifo_out.c
 libarts_xine_la_LDFLAGS = $(all_libraries) -module -no-undefined -pthread
-libarts_xine_la_LIBADD = $(XINE_LIBS) $(LIB_X11) $(LIB_XEXT) \
+libarts_xine_la_LIBADD = $(XINE_LIBS) $(LIBPTHREAD) $(LIB_X11) $(LIB_XEXT) \
 			 -lkmedia2_idl -lsoundserver_idl -lartsflow
 
 libarts_xine_la_METASOURCES = AUTO