Rollup merge of #80534 - LeSeulArtichaut:doc-include, r=jyn514

Use #[doc = include_str!()] in std

cc https://github.com/rust-lang/rust/issues/78835#issuecomment-742531894
r? `````@jyn514`````

library/core/src/macros/mod.rs

@@ -1,4 +1,4 @@
-#[doc(include = "panic.md")]
+#[doc = include_str!("panic.md")]
 #[macro_export]
 #[rustc_builtin_macro = "core_panic"]
 #[allow_internal_unstable(edition_panic)]

library/std/src/lib.rs

@@ -264,7 +264,6 @@
 #![feature(exhaustive_patterns)]
 #![feature(extend_one)]
 #![feature(extended_key_value_attributes)]
-#![feature(external_doc)]
 #![feature(fn_traits)]
 #![feature(format_args_nl)]
 #![feature(gen_future)]

library/std/src/macros.rs

@@ -4,7 +4,7 @@
 //! library. Each macro is available for use when linking against the standard
 //! library.
 
-#[doc(include = "../../core/src/macros/panic.md")]
+#[doc = include_str!("../../core/src/macros/panic.md")]
 #[macro_export]
 #[rustc_builtin_macro = "std_panic"]
 #[stable(feature = "rust1", since = "1.0.0")]

library/std/src/os/raw/mod.rs

@@ -18,7 +18,7 @@ macro_rules! type_alias_no_nz {
       $Docfile:tt, $Alias:ident = $Real:ty;
       $( $Cfg:tt )*
     } => {
-        #[doc(include = $Docfile)]
+        #[doc = include_str!($Docfile)]
         $( $Cfg )*
         #[stable(feature = "raw_os", since = "1.1.0")]
         pub type $Alias = $Real;