Add extern crate rustc_driver to proc-macro-srv-cli

Author: Veykril

src/tools/rust-analyzer/crates/proc-macro-srv-cli/src/main.rs

@@ -1,5 +1,8 @@
 //! A standalone binary for `proc-macro-srv`.
 //! Driver for proc macro server
+#[cfg(feature = "in-rust-tree")]
+extern crate rustc_driver as _;
+
 use std::io;
 
 fn main() -> std::io::Result<()> {

src/tools/rust-analyzer/crates/rust-analyzer/src/bin/main.rs

@@ -5,8 +5,7 @@
 #![warn(rust_2018_idioms, unused_lifetimes)]
 #![cfg_attr(feature = "in-rust-tree", feature(rustc_private))]
 #[cfg(feature = "in-rust-tree")]
-#[allow(unused_extern_crates)]
-extern crate rustc_driver;
+extern crate rustc_driver as _;
 
 mod logger;
 mod rustc_wrapper;