stage2: fix returning structs byval from functions

test/behavior/struct.zig

@@ -129,3 +129,18 @@ const MemberFnRand = struct {
         return r.seed;
     }
 };
+
+test "return struct byval from function" {
+    const bar = makeBar2(1234, 5678);
+    try expect(bar.y == 5678);
+}
+const Bar = struct {
+    x: i32,
+    y: i32,
+};
+fn makeBar2(x: i32, y: i32) Bar {
+    return Bar{
+        .x = x,
+        .y = y,
+    };
+}