use HOSTCFLAGS, avoid object file generation

target/tools/mkfimage/Makefile

@@ -1,4 +1,4 @@
 include $(TOPDIR)/rules.mk
 
 all:
-	$(HOSTCC) -o ${STAGING_HOST_DIR}/bin/mkfimage mkfimage.c
+	$(HOSTCC) ${HOSTCFLAGS} -o ${STAGING_HOST_DIR}/bin/mkfimage mkfimage.c

target/tools/trx/Makefile

@@ -1,4 +1,4 @@
 include $(TOPDIR)/rules.mk
 
 all:
-	$(HOSTCC) -o ${STAGING_HOST_DIR}/bin/trx trx.c
+	$(HOSTCC) ${HOSTCFLAGS} -o ${STAGING_HOST_DIR}/bin/trx trx.c

target/tools/uboot-mkimage/Makefile

@@ -1,6 +1,4 @@
 include $(TOPDIR)/rules.mk
 
 all:
-	$(HOSTCC) -c crc32.c -o crc32.o
-	$(HOSTCC) -c mkimage.c -o mkimage.o
-	$(HOSTCC) -o ${STAGING_HOST_DIR}/bin/mkimage mkimage.o crc32.o
+	$(HOSTCC) ${HOSTCFLAGS} -o ${STAGING_HOST_DIR}/bin/mkimage mkimage.c crc32.c