library.mak: only run asm strip if ASMSTRIP flags are set

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

library.mak

@@ -25,7 +25,7 @@ $(SUBDIR)%-test.i: $(SUBDIR)%.c
 $(SUBDIR)x86/%.o: $(SUBDIR)x86/%.asm
 	$(DEPYASM) $(YASMFLAGS) -I $(<D)/ -M -o $@ $< > $(@:.o=.d)
 	$(YASM) $(YASMFLAGS) -I $(<D)/ -o $@ $<
-	-$(STRIP) $(ASMSTRIPFLAGS) $@
+	-$(if $(ASMSTRIPFLAGS), $(STRIP) $(ASMSTRIPFLAGS) $@)
 
 LIBOBJS := $(OBJS) $(SUBDIR)%.h.o $(TESTOBJS)
 $(LIBOBJS) $(LIBOBJS:.o=.s) $(LIBOBJS:.o=.i):   CPPFLAGS += -DHAVE_AV_CONFIG_H