Ignore doctest for GATs

Author: lowr

chalk-solve/src/rust_ir.rs

@@ -214,10 +214,11 @@ pub struct FnDefDatumBound<I: Interner> {
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
+// FIXME: unignore the doctest below when GATs hit stable.
 /// A rust intermediate representation (rust_ir) of a Trait Definition. For
 /// example, given the following rust code:
 ///
-/// ```compile_fail
+/// ```ignore
 /// use std::fmt::Debug;
 ///
 /// trait Foo<T>