Auto merge of #45451 - durka:patch-45, r=steveklabnik

fix stringify docs

Update `stringify!` docs to show actual accepted syntax. Reported [on reddit](https://www.reddit.com/r/rust/comments/76o8rh/hey_rustaceans_got_an_easy_question_ask_here/dopzwys/).

Author: bors

src/libcore/macros.rs

@@ -682,15 +682,15 @@ mod builtin {
     #[cfg(dox)]
     macro_rules! file { () => ({ /* compiler built-in */ }) }
 
-    /// A macro which stringifies its argument.
+    /// A macro which stringifies its arguments.
     ///
     /// For more information, see the documentation for [`std::stringify!`].
     ///
     /// [`std::stringify!`]: ../std/macro.stringify.html
     #[stable(feature = "rust1", since = "1.0.0")]
     #[macro_export]
     #[cfg(dox)]
-    macro_rules! stringify { ($t:tt) => ({ /* compiler built-in */ }) }
+    macro_rules! stringify { ($($t:tt)*) => ({ /* compiler built-in */ }) }
 
     /// Includes a utf8-encoded file as a string.
     ///

src/libstd/macros.rs

@@ -490,7 +490,7 @@ pub mod builtin {
     #[macro_export]
     macro_rules! file { () => ({ /* compiler built-in */ }) }
 
-    /// A macro which stringifies its argument.
+    /// A macro which stringifies its arguments.
     ///
     /// This macro will yield an expression of type `&'static str` which is the
     /// stringification of all the tokens passed to the macro. No restrictions
@@ -507,7 +507,7 @@ pub mod builtin {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[macro_export]
-    macro_rules! stringify { ($t:tt) => ({ /* compiler built-in */ }) }
+    macro_rules! stringify { ($($t:tt)*) => ({ /* compiler built-in */ }) }
 
     /// Includes a utf8-encoded file as a string.
     ///