tcg/optimize: Use fold_masks_z in fold_setcond2

Avoid the use of the OptContext slots.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tcg/optimize.c

@@ -2468,8 +2468,7 @@ static bool fold_setcond2(OptContext *ctx, TCGOp *op)
         return fold_setcond(ctx, op);
     }
 
-    ctx->z_mask = 1;
-    return false;
+    return fold_masks_z(ctx, op, 1);
 
  do_setcond_const:
     return tcg_opt_gen_movi(ctx, op, op->args[0], i);