Link std statically in rustc_driver

Author: Zoxc

Diff for: src/git-rustfmt/main.rs

@@ -1,3 +1,7 @@
+// We need this feature as it changes `dylib` linking behavior and allows us to link to
+// `rustc_driver`.
+#![feature(rustc_private)]
+
 #[macro_use]
 extern crate tracing;