Fix building of object files in tools/

Fixes issue issue2408.

Originally committed as revision 25905 to svn://svn.ffmpeg.org/ffmpeg/trunk

Makefile

@@ -90,7 +90,7 @@ tools/%$(EXESUF): tools/%.o
 	$(LD) $(FF_LDFLAGS) -o $@ $< $(FF_EXTRALIBS)
 
 tools/%.o: tools/%.c
-	$(CC) $(CPPFLAGS) $(CFLAGS) $(CC_O) $<
+	$(CC) $(CPPFLAGS) $(CFLAGS) -c $(CC_O) $<
 
 ffplay.o: CFLAGS += $(SDL_CFLAGS)