Auto merge of rust-lang#16249 - lnicola:sync-from-rust, r=lnicola

internal: Sync from rust

Author: bors

crates/proc-macro-srv/proc-macro-test/imp/src/lib.rs

@@ -1,5 +1,7 @@
 //! Exports a few trivial procedural macros for testing.
 
+#![allow(unexpected_cfgs)]
+#![cfg(feature = "sysroot-abi")]
 #![cfg(any(feature = "sysroot-abi", rust_analyzer))]
 #![warn(rust_2018_idioms, unused_lifetimes)]
 #![feature(proc_macro_span, proc_macro_def_site)]