fix(stageleft_tool): avoid generating warnings for unexpected `stagel…

…eft_devel` feature (hydro-project#1643)

Crates using stageleft can always be safely built without ever touching
this feature, it's only used as a helper to improve incremental
compilation performance for non-library crates.

Co-authored-by: Mingwei Samuel <mingwei.samuel@gmail.com>

stageleft_tool/src/lib.rs

@@ -329,6 +329,7 @@ pub fn gen_final_helper() {
 #[macro_export]
 macro_rules! gen_final {
     () => {
+        #[allow(unexpected_cfgs)]
         #[cfg(not(feature = "stageleft_devel"))]
         $crate::gen_final_helper()
     };