build: move COLO under CONFIG_REPLICATION

We don't allow to use x-colo capability when replication is not
configured. So, no reason to build COLO when replication is disabled,
it's unusable in this case.

Note also that the check in migrate_caps_check() is not the only
restriction: some functions in migration/colo.c will just abort if
called with not defined CONFIG_REPLICATION, for example:

    migration_iteration_finish()
       case MIGRATION_STATUS_COLO:
           migrate_start_colo_process()
               colo_process_checkpoint()
                   abort()

It could probably make sense to have possibility to enable COLO without
REPLICATION, but this requires deeper audit of colo & replication code,
which may be done later if needed.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Acked-by: Dr. David Alan Gilbert <dave@treblig.org>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Message-Id: <20230428194928.1426370-4-vsementsov@yandex-team.ru>
Signed-off-by: Juan Quintela <quintela@redhat.com>

stubs/colo.c

@@ -0,0 +1,39 @@
+#include "qemu/osdep.h"
+#include "qemu/notify.h"
+#include "net/colo-compare.h"
+#include "migration/colo.h"
+#include "migration/migration.h"
+#include "qemu/error-report.h"
+#include "qapi/qapi-commands-migration.h"
+
+void colo_shutdown(void)
+{
+}
+
+void *colo_process_incoming_thread(void *opaque)
+{
+    error_report("Impossible happend: trying to start COLO thread when COLO "
+                 "module is not built in");
+    abort();
+}
+
+void colo_checkpoint_delay_set(void)
+{
+}
+
+void migrate_start_colo_process(MigrationState *s)
+{
+    error_report("Impossible happend: trying to start COLO when COLO "
+                 "module is not built in");
+    abort();
+}
+
+bool migration_in_colo_state(void)
+{
+    return false;
+}
+
+bool migration_incoming_in_colo_state(void)
+{
+    return false;
+}

stubs/meson.build

@@ -45,6 +45,7 @@ stub_ss.add(files('target-get-monitor-def.c'))
 stub_ss.add(files('target-monitor-defs.c'))
 stub_ss.add(files('trace-control.c'))
 stub_ss.add(files('uuid.c'))
+stub_ss.add(files('colo.c'))
 stub_ss.add(files('vmstate.c'))
 stub_ss.add(files('vm-stop.c'))
 stub_ss.add(files('win32-kbd-hook.c'))