migration: introduce VMSTATE_BUFFER_UNSAFE_INFO_TEST()

There is no _TEST() variant of VMSTATE_BUFFER_UNSAFE_INFO() yet, but we'll
soon need it. Introduce it and rebase the original
VMSTATE_BUFFER_UNSAFE_INFO() on top.

The parameter order of the new function-like macro follows that of
VMSTATE_SINGLE_TEST(): "_test" is introduced between "_state" and
"_version".

Cc: Juan Quintela <quintela@redhat.com>
Cc: Amit Shah <amit.shah@redhat.com>
Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: NLaszlo Ersek <lersek@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

include/migration/vmstate.h

@@ -500,9 +500,10 @@ extern const VMStateInfo vmstate_info_bitmap;
     .start        = (_start),                                        \
 }
 
-#define VMSTATE_BUFFER_UNSAFE_INFO(_field, _state, _version, _info, _size) { \
+#define VMSTATE_BUFFER_UNSAFE_INFO_TEST(_field, _state, _test, _version, _info, _size) { \
     .name       = (stringify(_field)),                               \
     .version_id = (_version),                                        \
+    .field_exists = (_test),                                         \
     .size       = (_size),                                           \
     .info       = &(_info),                                          \
     .flags      = VMS_BUFFER,                                        \
@@ -562,6 +563,10 @@ extern const VMStateInfo vmstate_info_bitmap;
     VMSTATE_STRUCT_ARRAY_TEST(_field, _state, _num, NULL, _version,   \
             _vmsd, _type)
 
+#define VMSTATE_BUFFER_UNSAFE_INFO(_field, _state, _version, _info, _size) \
+    VMSTATE_BUFFER_UNSAFE_INFO_TEST(_field, _state, NULL, _version, _info, \
+            _size)
+
 #define VMSTATE_BOOL_V(_f, _s, _v)                                    \
     VMSTATE_SINGLE(_f, _s, _v, vmstate_info_bool, bool)