Rollup merge of #23056 - awlnx:master, r=nrc

src/liballoc/lib.rs

@@ -56,6 +56,8 @@
 //! The [`heap`](heap/index.html) module defines the low-level interface to the
 //! default global allocator. It is not compatible with the libc allocator API.
 
+// Do not remove on snapshot creation. Needed for bootstrap. (Issue #22364)
+#![cfg_attr(stage0, feature(custom_attribute))]
 #![crate_name = "alloc"]
 #![unstable(feature = "alloc")]
 #![feature(staged_api)]