Add runtime check to avoid overwrite arg easily in diag and store and restore snapshot when set subdiag arg

Signed-off-by: xizheyin <xizheyin@smail.nju.edu.cn>

compiler/rustc_builtin_macros/src/errors.rs

@@ -672,6 +672,7 @@ impl Subdiagnostic for FormatUnusedArg {
     fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         diag.arg("named", self.named);
         let msg = diag.eagerly_translate(crate::fluent_generated::builtin_macros_format_unused_arg);
+        diag.remove_arg("named");
         diag.span_label(self.span, msg);
     }
 }