Mention implementers of unsatisfied trait

When encountering an unsatisfied trait bound, if there are no other
suggestions, mention all the types that *do* implement that trait:

```
error[E0277]: the trait bound `f32: Foo` is not satisfied
  --> $DIR/impl_wf.rs:22:6
   |
LL | impl Baz<f32> for f32 { }
   |      ^^^^^^^^ the trait `Foo` is not implemented for `f32`
   |
   = help: the following other types implement trait `Foo`:
             Option<T>
             i32
             str
note: required by a bound in `Baz`
  --> $DIR/impl_wf.rs:18:31
   |
LL | trait Baz<U: ?Sized> where U: Foo { }
   |                               ^^^ required by this bound in `Baz`
```

Mention implementers of traits in `ImplObligation`s.

Do not mention other `impl`s for closures, ranges and `?`.

compiler/rustc_middle/src/ty/mod.rs

@@ -41,7 +41,7 @@ use rustc_hir::Node;
 use rustc_macros::HashStable;
 use rustc_query_system::ich::StableHashingContext;
 use rustc_session::cstore::CrateStoreDyn;
-use rustc_span::symbol::{kw, Ident, Symbol};
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::Span;
 use rustc_target::abi::Align;
 
@@ -2206,7 +2206,7 @@ impl<'tcx> TyCtxt<'tcx> {
         self.impl_trait_ref(def_id).map(|tr| tr.def_id)
     }
 
-    /// If the given defid describes a method belonging to an impl, returns the
+    /// If the given `DefId` describes a method belonging to an impl, returns the
     /// `DefId` of the impl that the method belongs to; otherwise, returns `None`.
     pub fn impl_of_method(self, def_id: DefId) -> Option<DefId> {
         self.opt_associated_item(def_id).and_then(|trait_item| match trait_item.container {
@@ -2215,6 +2215,11 @@ impl<'tcx> TyCtxt<'tcx> {
         })
     }
 
+    /// If the given `DefId` belongs to a trait that was automatically derived, returns `true`.
+    pub fn is_builtin_derive(self, def_id: DefId) -> bool {
+        self.has_attr(def_id, sym::automatically_derived)
+    }
+
     /// Looks up the span of `impl_did` if the impl is local; otherwise returns `Err`
     /// with the name of the crate containing the impl.
     pub fn span_of_impl(self, impl_did: DefId) -> Result<Span, Symbol> {