Make Lazy not care about lifetimes until decode

compiler/rustc_middle/src/lib.rs

@@ -33,6 +33,7 @@
 #![feature(discriminant_kind)]
 #![feature(exhaustive_patterns)]
 #![feature(get_mut_unchecked)]
+#![feature(generic_associated_types)]
 #![feature(if_let_guard)]
 #![feature(map_first_last)]
 #![feature(negative_impls)]