Rollup merge of rust-lang#56738 - turboladen:fix-private_no_mangle_fns-message, r=zackmdavis

Fix private_no_mangle_fns message grammar

Simply changes "an warning" to "a warning" in the `private_no_mangle_fns` warning. I started getting this in some code after upgrading to 1.31.0.

Author: pietroalbini

src/librustc_lint/lib.rs

@@ -376,7 +376,7 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
     store.register_removed("resolve_trait_on_defaulted_unit",
         "converted into hard error, see https://github.com/rust-lang/rust/issues/48950");
     store.register_removed("private_no_mangle_fns",
-        "no longer an warning, #[no_mangle] functions always exported");
+        "no longer a warning, #[no_mangle] functions always exported");
     store.register_removed("private_no_mangle_statics",
-        "no longer an warning, #[no_mangle] statics always exported");
+        "no longer a warning, #[no_mangle] statics always exported");
 }

src/test/ui/lint/lint-unexported-no-mangle.stderr

@@ -1,8 +1,8 @@
-warning: lint `private_no_mangle_fns` has been removed: `no longer an warning, #[no_mangle] functions always exported`
+warning: lint `private_no_mangle_fns` has been removed: `no longer a warning, #[no_mangle] functions always exported`
    |
    = note: requested on the command line with `-F private_no_mangle_fns`
 
-warning: lint `private_no_mangle_statics` has been removed: `no longer an warning, #[no_mangle] statics always exported`
+warning: lint `private_no_mangle_statics` has been removed: `no longer a warning, #[no_mangle] statics always exported`
    |
    = note: requested on the command line with `-F private_no_mangle_statics`