add regression test for issue rust-lang#39161

Author: yerke

src/test/ui/consts/issue-39161-bogus-error.rs

@@ -0,0 +1,13 @@
+// check-pass
+
+pub struct X {
+    pub a: i32,
+    pub b: i32,
+}
+
+fn main() {
+    const DX: X = X { a: 0, b: 0 };
+    const _X1: X = X { a: 1, ..DX };
+    let _x2 = X { a: 1, b: 2, ..DX };
+    const _X3: X = X { a: 1, b: 2, ..DX };
+}