Add a regression test

Author: oli-obk

Diff for: src/test/ui/type-alias-impl-trait/different_defining_uses_never_type3.rs

@@ -0,0 +1,12 @@
+#![feature(type_alias_impl_trait)]
+
+type Tait = impl Sized;
+
+struct One;
+fn one() -> Tait { One }
+
+struct Two<T>(T);
+fn two() -> Tait { Two::<()>(todo!()) }
+//~^ ERROR concrete type differs from previous defining opaque type use
+
+fn main() {}

Diff for: src/test/ui/type-alias-impl-trait/different_defining_uses_never_type3.stderr

@@ -0,0 +1,14 @@
+error: concrete type differs from previous defining opaque type use
+  --> $DIR/different_defining_uses_never_type3.rs:9:13
+   |
+LL | fn two() -> Tait { Two::<()>(todo!()) }
+   |             ^^^^ expected `One`, got `Two<()>`
+   |
+note: previous use here
+  --> $DIR/different_defining_uses_never_type3.rs:6:20
+   |
+LL | fn one() -> Tait { One }
+   |                    ^^^
+
+error: aborting due to previous error
+