target/i386: optimize cross-page direct jumps in softmmu

Instead of unconditionally exiting to the exec loop, use the
gen_jr helper to jump to the target if it is valid.

Perf impact: see next commit's log.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1493263764-18657-10-git-send-email-cota@braap.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>

target/i386/translate.c

@@ -2154,9 +2154,9 @@ static inline void gen_goto_tb(DisasContext *s, int tb_num, target_ulong eip)
         gen_jmp_im(eip);
         tcg_gen_exit_tb((uintptr_t)s->tb + tb_num);
     } else {
-        /* jump to another page: currently not optimized */
+        /* jump to another page */
         gen_jmp_im(eip);
-        gen_eob(s);
+        gen_jr(s, cpu_tmp0);
     }
 }