replay: do not build if TCG is not available

this fixes non-TCG builds broken recently by replay reverse debugging.

Stub the needed functions in stub/, splitting roughly between functions
needed only by system emulation, by system emulation and tools,
and by everyone.  This includes duplicating some code in replay/, and
puts the logic for non-replay related events in the replay/ module (+
the stubs), so this should be revisited in the future.

Surprisingly, only _one_ qtest was affected by this, ide-test.c, which
resulted in a buzz as the bh events were never delivered, and the bh
never executed.

Many other subsystems _should_ have been affected.

This fixes the immediate issue, however a better way to group replay
functionality to TCG-only code could be developed in the long term.

Signed-off-by: Claudio Fontana <cfontana@suse.de>
Message-Id: <20201013192123.22632-4-cfontana@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

stubs/replay-tools.c

@@ -0,0 +1,83 @@
+#include "qemu/osdep.h"
+#include "sysemu/replay.h"
+#include "block/aio.h"
+
+bool replay_events_enabled(void)
+{
+    return false;
+}
+
+int64_t replay_save_clock(unsigned int kind, int64_t clock, int64_t raw_icount)
+{
+    abort();
+    return 0;
+}
+
+int64_t replay_read_clock(unsigned int kind)
+{
+    abort();
+    return 0;
+}
+
+uint64_t replay_get_current_icount(void)
+{
+    return 0;
+}
+
+void replay_bh_schedule_event(QEMUBH *bh)
+{
+    qemu_bh_schedule(bh);
+}
+
+void replay_bh_schedule_oneshot_event(AioContext *ctx,
+     QEMUBHFunc *cb, void *opaque)
+{
+    aio_bh_schedule_oneshot(ctx, cb, opaque);
+}
+
+bool replay_checkpoint(ReplayCheckpoint checkpoint)
+{
+    return true;
+}
+
+void replay_mutex_lock(void)
+{
+}
+
+void replay_mutex_unlock(void)
+{
+}
+
+void replay_register_char_driver(Chardev *chr)
+{
+}
+
+void replay_chr_be_write(Chardev *s, uint8_t *buf, int len)
+{
+    abort();
+}
+
+void replay_char_write_event_save(int res, int offset)
+{
+    abort();
+}
+
+void replay_char_write_event_load(int *res, int *offset)
+{
+    abort();
+}
+
+int replay_char_read_all_load(uint8_t *buf)
+{
+    abort();
+}
+
+void replay_char_read_all_save_error(int res)
+{
+    abort();
+}
+
+void replay_char_read_all_save_buf(uint8_t *buf, int offset)
+{
+    abort();
+}