Resolved some of the comments

* Undo fn -> const fn for some fns.
* Split feature gate.
* Made all three intrinsics const

library/core/src/lib.rs

@@ -69,6 +69,7 @@
 #![feature(asm)]
 #![feature(cfg_target_has_atomic)]
 #![feature(const_alloc_layout)]
+#![feature(const_assert_type)]
 #![feature(const_discriminant)]
 #![feature(const_cell_into_inner)]
 #![feature(const_checked_int_methods)]
@@ -101,7 +102,7 @@
 #![feature(const_type_name)]
 #![feature(const_likely)]
 #![feature(const_unreachable_unchecked)]
-#![feature(const_maybe_assume_init)]
+#![feature(const_maybe_uninit_assume_init)]
 #![feature(custom_inner_attributes)]
 #![feature(decl_macro)]
 #![feature(doc_cfg)]