run_make_support: add #![warn(unreachable_pub)]

src/tools/run-make-support/src/lib.rs

@@ -6,6 +6,7 @@
 // We want to control use declaration ordering and spacing (and preserve use group comments), so
 // skip rustfmt on this file.
 #![cfg_attr(rustfmt, rustfmt::skip)]
+#![warn(unreachable_pub)]
 
 mod command;
 mod macros;