tcg: Add generic DISAS_NORETURN

This will allow some amount of cleanup to happen before
switching the backends over to enum DisasJumpType.

Reviewed-by: Emilio G. Cota <cota@braap.org>
Reviewed-by: Lluís Vilanova <vilanova@ac.upc.edu>
Signed-off-by: Richard Henderson <rth@twiddle.net>

include/exec/exec-all.h

@@ -63,6 +63,7 @@ typedef ram_addr_t tb_page_addr_t;
 #define DISAS_JUMP    1 /* only pc was modified dynamically */
 #define DISAS_TB_JUMP 2 /* only pc was modified statically */
 #define DISAS_UPDATE  3 /* cpu state was modified dynamically */
+#define DISAS_NORETURN 4 /* the tb has already been exited */
 
 #include "qemu/log.h"