Allow unreachable_patterns instead of using if true

src/librustc_mir/interpret/validity.rs

@@ -59,7 +59,8 @@ macro_rules! try_validation_pat {
             Ok(x) => x,
             // We catch the error and turn it into a validation failure. We are okay with
             // allocation here as this can only slow down builds that fail anyway.
-            $( Err(InterpErrorInfo { kind: $p, .. }) )|* if true => throw_validation_failure!($what, $where $(, $details)?),
+            $( Err(InterpErrorInfo { kind: $p, .. }) )|* => throw_validation_failure!($what, $where $(, $details)?),
+            #[allow(unreachable_patterns)]
             Err(e) => Err::<!, _>(e)?,
         }
     }};