tools/virtio: enable to build with retpoline

Add build options to bring it close to a linux kernel. It allows for
testing that is close to reality.
Signed-off-by: Shunsuke Mie <mie@igel.co.jp>
Message-Id: <20230202104538.2041879-1-mie@igel.co.jp>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

tools/virtio/Makefile

@@ -4,7 +4,7 @@ test: virtio_test vringh_test
 virtio_test: virtio_ring.o virtio_test.o
 vringh_test: vringh_test.o vringh.o virtio_ring.o
 
-CFLAGS += -g -O2 -Werror -Wno-maybe-uninitialized -Wall -I. -I../include/ -I ../../usr/include/ -Wno-pointer-sign -fno-strict-overflow -fno-strict-aliasing -fno-common -MMD -U_FORTIFY_SOURCE -include ../../include/linux/kconfig.h
+CFLAGS += -g -O2 -Werror -Wno-maybe-uninitialized -Wall -I. -I../include/ -I ../../usr/include/ -Wno-pointer-sign -fno-strict-overflow -fno-strict-aliasing -fno-common -MMD -U_FORTIFY_SOURCE -include ../../include/linux/kconfig.h -mfunction-return=thunk -fcf-protection=none -mindirect-branch-register
 CFLAGS += -pthread
 LDFLAGS += -pthread
 vpath %.c ../../drivers/virtio ../../drivers/vhost