Small fixes in Makefile

Makefile

@@ -1,7 +1,7 @@
 dev-image = 5150-dev
 
 %.bin: %.asm
-	nasm $? -o $@
+	nasm $< -o $@
 
 crc16.s: crc16.c
 	ia16-elf-gcc -S -Os -o crc16.s crc16.c
@@ -19,10 +19,13 @@ LDFLAGS = -mregparmcall -Wl,--gc-sections -Os -nostdlib -flto
 %.elf:
 	$(LD) $(LDFLAGS) $(CPPFLAGS) -o $@ $^
 
+%.com: %.elf
+	ia16-elf-objcopy -O binary $< $@
+
 bootsectors = fat12boot.bin wozmon.bin
 
 $(bootsectors):
-	ia16-elf-objcopy -O binary $? $@
+	ia16-elf-objcopy -O binary $< $@
 	truncate -s 510 $@
 	printf "\125\252" >> $@
 
@@ -34,8 +37,6 @@ fat12boot.bin: fat12boot.elf
 polmon.elf: LDFLAGS += -T flat0600.ld
 polmon.elf: polmon.o
 
-polmon.com: polmon.elf
-	ia16-elf-objcopy -O binary $? $@
 
 wozmon.o: polmon.cc
 wozmon.o: CPPFLAGS = -DWOZMON=1
@@ -48,15 +49,16 @@ wozmon.elf: CPPFLAGS += -DNOBPB
 
 wozmon.bin: wozmon.elf
 
-polos.img: fat12boot.bin polmon.com
+polos.img: fat12boot.bin polmon.com polio.com
 	dd if=/dev/zero of=$@ bs=512 count=720
 	mformat -i $@ -t 40 -h 2 -s 9
+	mcopy -i $@ polio.com ::/polio.com
 	mcopy -i $@ polmon.com ::/polmon.com
 	dd if=fat12boot.bin of=$@ conv=notrunc
 
 .PHONY: clean
 clean:			## Remove generated files
-	rm -rf *.bin polmon.com polos.img
+	rm -rf *.bin *.elf *.o *.com polos.img
 
 .PHONY: dev-image
 dev-image: