tests: fix linking test-char on win32

test.char.exe fails to link:
qemu-char.o: In function `win_chr_free':
/home/elmarco/src/qemu/qemu-char.c:2149: undefined reference to `qemu_del_polling_cb'
/home/elmarco/src/qemu/qemu-char.c:2151: undefined reference to `qemu_del_polling_cb'
qemu-char.o: In function `win_stdio_thread':
/home/elmarco/src/qemu/qemu-char.c:2568: undefined reference to `qemu_del_wait_object'
qemu-char.o: In function `qemu_chr_open_stdio':
/home/elmarco/src/qemu/qemu-char.c:2661: undefined reference to `qemu_add_wait_object'
/home/elmarco/src/qemu/qemu-char.c:2646: undefined reference to
`qemu_add_wait_object'
...

It needs main-loop.o symbols, among others. Linking with
$(test-block-obj-y) brings what's necessary. We could try to eventually
strip to the minimum if needed.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

tests/Makefile.include

@@ -510,7 +510,7 @@ tests/check-qjson$(EXESUF): tests/check-qjson.o $(test-util-obj-y)
 tests/check-qom-interface$(EXESUF): tests/check-qom-interface.o $(test-qom-obj-y)
 tests/check-qom-proplist$(EXESUF): tests/check-qom-proplist.o $(test-qom-obj-y)
 
-tests/test-char$(EXESUF): tests/test-char.o qemu-char.o qemu-timer.o $(test-util-obj-y) $(qtest-obj-y) $(test-io-obj-y)
+tests/test-char$(EXESUF): tests/test-char.o qemu-char.o qemu-timer.o $(test-util-obj-y) $(qtest-obj-y) $(test-block-obj-y)
 tests/test-coroutine$(EXESUF): tests/test-coroutine.o $(test-block-obj-y)
 tests/test-aio$(EXESUF): tests/test-aio.o $(test-block-obj-y)
 tests/test-throttle$(EXESUF): tests/test-throttle.o $(test-block-obj-y)