Add a new rustc_driver dylib to rexport rustc_driver_impl

compiler/rustc_driver/src/lib.rs

@@ -0,0 +1,7 @@
+// This crate is intentionally empty and a rexport of `rustc_driver_impl` to allow the code in
+// `rustc_driver_impl` to be compiled in parallel with other crates.
+
+#![allow(unused_extern_crates)]
+extern crate rustc_driver_impl;
+
+pub use rustc_driver_impl::*;