Fixes in various places

Author: Nadrieril

src/eval.rs

@@ -463,6 +463,7 @@ pub fn eval_entry<'tcx>(
     let res = match res {
         Err(res) => res,
         // `Ok` can never happen
+        #[cfg(bootstrap)]
         Ok(never) => match never {},
     };
 

tests/pass/async-fn.rs

@@ -59,6 +59,7 @@ async fn hello_world() {
 }
 
 // This example comes from https://github.com/rust-lang/rust/issues/115145
+#[allow(unreachable_patterns)]
 async fn uninhabited_variant() {
     async fn unreachable(_: Never) {}
 

tests/pass/enums.rs

@@ -43,6 +43,7 @@ fn discriminant_overflow() {
     }
 }
 
+#[allow(unreachable_patterns)]
 fn more_discriminant_overflow() {
     pub enum Infallible {}