fix accidental inclusion of SDL_Mixer for wad creation

Index: data/Makefile.in
--- data/Makefile.in.orig
+++ data/Makefile.in
@@ -689,7 +689,7 @@ clean-noinstPROGRAMS:
 
 rdatawad$(EXEEXT): $(rdatawad_OBJECTS) $(rdatawad_DEPENDENCIES) $(EXTRA_rdatawad_DEPENDENCIES) 
 	@rm -f rdatawad$(EXEEXT)
-	$(AM_V_CCLD)$(LINK) $(rdatawad_OBJECTS) $(rdatawad_LDADD) $(LIBS)
+	$(AM_V_CCLD)$(LINK) $(rdatawad_OBJECTS) $(rdatawad_LDADD)
 
 mostlyclean-compile:
 	-rm -f *.$(OBJEXT)
