tools/virtio: virtio_test tool

This is the userspace part of the tool: it includes a bunch of stubs for
linux APIs, somewhat simular to linuxsched. This makes it possible to
recompile the ring code in userspace.

A small test example is implemented combining this with vhost_test
module.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

tools/virtio/Makefile

@@ -0,0 +1,12 @@
+all: test mod
+test: virtio_test
+virtio_test: virtio_ring.o virtio_test.o
+CFLAGS += -g -O2 -Wall -I. -I ../../usr/include/ -Wno-pointer-sign -fno-strict-overflow  -MMD
+vpath %.c ../../drivers/virtio
+mod:
+	${MAKE} -C `pwd`/../.. M=`pwd`/vhost_test
+.PHONY: all test mod clean
+clean:
+	${RM} *.o vhost_test/*.o vhost_test/.*.cmd \
+              vhost_test/Module.symvers vhost_test/modules.order *.d
+-include *.d