pc-bios/s390-ccw.img: Fix build

Since
commit a9c87304 ("build-sys: fix building with make CFLAGS=.. argument")

pc-bios/s390-ccw.img build might fail with

--- snip ---
main.o: In function `virtio_setup':
qemu/pc-bios/s390-ccw/main.c:117: undefined reference to `__stack_chk_fail'
--- snip ---

Changing the CFLAGS to QEMU_CFLAGS does the trick. We also need to
add -fno-strict-aliasing as this was filtered out.
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <1471258997-5811-1-git-send-email-borntraeger@de.ibm.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>

pc-bios/s390-ccw/Makefile

@@ -10,8 +10,10 @@ $(call set-vpath, $(SRC_PATH)/pc-bios/s390-ccw)
 .PHONY : all clean build-all
 
 OBJECTS = start.o main.o bootmap.o sclp-ascii.o virtio.o virtio-scsi.o
-CFLAGS += -fPIE -fno-stack-protector -ffreestanding -march=z900
-CFLAGS += -fno-delete-null-pointer-checks -msoft-float
+QEMU_CFLAGS := $(filter -W%, $(QEMU_CFLAGS))
+QEMU_CFLAGS += -ffreestanding -fno-delete-null-pointer-checks -msoft-float
+QEMU_CFLAGS += -march=z900 -fPIE -fno-strict-aliasing
+QEMU_CFLAGS += $(call cc-option, $(QEMU_CFLAGS), -fno-stack-protector)
 LDFLAGS += -Wl,-pie -nostdlib
 
 build-all: s390-ccw.img