otionrom: Use local CFLAGS no global one

It is needed by %.o : %.c rule.
Signed-off-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

pc-bios/optionrom/Makefile

@@ -10,6 +10,7 @@ VPATH=$(SRC_PATH)/pc-bios/optionrom
 CFLAGS = -Wall -Wstrict-prototypes -Werror -fomit-frame-pointer -fno-builtin
 CFLAGS += -I$(SRC_PATH)
 CFLAGS += $(call cc-option, -fno-stack-protector,"")
+QEMU_CFLAGS = $(CFLAGS)
 
 build-all: multiboot.bin