gccrs: Add new check for contains_associated_types

We don't need to setup associated types when a trait does not contain any
associated types.

gcc/rust/ChangeLog:

	* typecheck/rust-tyty-bounds.cc (TypeBoundPredicate::contains_associated_types):
	Check if a type bound predicate contains assocated types.
	* typecheck/rust-tyty.h: Declare the above mentioned function.
	* typecheck/rust-hir-trait-resolve.cc: Use `contains_associated_types`
	function.

gcc/rust/typecheck/rust-hir-trait-resolve.cc

@@ -368,6 +368,9 @@ void
 AssociatedImplTrait::setup_associated_types (
   const TyTy::BaseType *self, const TyTy::TypeBoundPredicate &bound)
 {
+  if (!bound.contains_associated_types ())
+    return;
+
   // compute the constrained impl block generic arguments based on self and the
   // higher ranked trait bound
   TyTy::BaseType *receiver = self->clone ();

gcc/rust/typecheck/rust-tyty-bounds.cc

@@ -374,6 +374,21 @@ TypeBoundPredicate::requires_generic_args () const
   return substitutions.size () > 1;
 }
 
+bool
+TypeBoundPredicate::contains_associated_types () const
+{
+  auto trait_ref = get ();
+  for (const auto &trait_item : trait_ref->get_trait_items ())
+    {
+      bool is_associated_type
+	= trait_item.get_trait_item_type ()
+	  == Resolver::TraitItemReference::TraitItemType::TYPE;
+      if (is_associated_type)
+	return true;
+    }
+  return false;
+}
+
 // trait item reference
 
 const Resolver::TraitItemReference *

gcc/rust/typecheck/rust-tyty.h

@@ -1057,6 +1057,8 @@ public:
 
   bool requires_generic_args () const;
 
+  bool contains_associated_types () const;
+
 private:
   DefId reference;
   Location locus;