Fix generation of config-host.h

This patch improves Anthony patch a6a853c8

Once there, it improves handling of object files for qemu tools

cc: Andreas Färber <andreas.faerber@web.de>
Signed-off-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

Makefile

@@ -126,21 +126,14 @@ bt-host.o: QEMU_CFLAGS += $(BLUEZ_CFLAGS)
 
 ######################################################################
 
-qemu-img.o: qemu-img-cmds.h config-host.h
+qemu-img.o: qemu-img-cmds.h
+qemu-img.o qemu-tool.o qemu-nbd.o qemu-io.o: $(GENERATED_HEADERS)
 
-obj-y = qemu-img.o qemu-tool.o $(block-obj-y) $(qobject-obj-y)
+qemu-img$(EXESUF): qemu-img.o qemu-tool.o $(block-obj-y) $(qobject-obj-y)
 
-qemu-img$(EXESUF): $(obj-y)
+qemu-nbd$(EXESUF): qemu-nbd.o qemu-tool.o $(block-obj-y) $(qobject-obj-y)
 
-obj-y = qemu-nbd.o qemu-tool.o $(block-obj-y) $(qobject-obj-y)
-$(obj-y): $(GENERATED_HEADERS)
-
-qemu-nbd$(EXESUF): $(obj-y)
-
-obj-y = qemu-io.o qemu-tool.o cmd.o $(block-obj-y) $(qobject-obj-y)
-$(obj-y): $(GENERATED_HEADERS)
-
-qemu-io$(EXESUF): $(obj-y)
+qemu-io$(EXESUF): qemu-io.o qemu-tool.o cmd.o $(block-obj-y) $(qobject-obj-y)
 
 qemu-img-cmds.h: $(SRC_PATH)/qemu-img-cmds.hx
 	$(call quiet-command,sh $(SRC_PATH)/hxtool -h < $< > $@,"  GEN   $@")