Treat TAIT equation as always ambiguous in coherence

tests/ui/from_over_into_unfixable.rs

@@ -32,10 +32,4 @@ impl Into<u8> for ContainsVal {
     }
 }
 
-type Opaque = impl Sized;
-struct IntoOpaque;
-impl Into<Opaque> for IntoOpaque {
-    fn into(self) -> Opaque {}
-}
-
 fn main() {}

tests/ui/from_over_into_unfixable.stderr

@@ -1,12 +1,29 @@
-error[E0658]: `impl Trait` in type aliases is unstable
-  --> $DIR/from_over_into_unfixable.rs:35:15
+error: an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true
+  --> $DIR/from_over_into_unfixable.rs:11:1
    |
-LL | type Opaque = impl Sized;
-   |               ^^^^^^^^^^
+LL | impl Into<InMacro> for String {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
-   = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
+   = help: replace the `Into` implementation with `From<std::string::String>`
+   = note: `-D clippy::from-over-into` implied by `-D warnings`
 
-error: aborting due to previous error
+error: an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true
+  --> $DIR/from_over_into_unfixable.rs:19:1
+   |
+LL | impl Into<WeirdUpperSelf> for &'static [u8] {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: replace the `Into` implementation with `From<&'static [u8]>`
+
+error: an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true
+  --> $DIR/from_over_into_unfixable.rs:28:1
+   |
+LL | impl Into<u8> for ContainsVal {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: `impl From<Local> for Foreign` is allowed by the orphan rules, for more information see
+           https://doc.rust-lang.org/reference/items/implementations.html#trait-implementation-coherence
+   = help: replace the `Into` implementation with `From<ContainsVal>`
+
+error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0658`.