tcg/optimize: Use fold_masks_s in fold_negsetcond

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

@@ -2387,8 +2387,7 @@ static bool fold_negsetcond(OptContext *ctx, TCGOp *op)
     }
 
     /* Value is {0,-1} so all bits are repetitions of the sign. */
-    ctx->s_mask = -1;
-    return false;
+    return fold_masks_s(ctx, op, -1);
 }
 
 static bool fold_setcond2(OptContext *ctx, TCGOp *op)