Fix builtin lints

compiler/rustc_lint/src/builtin.rs

@@ -975,10 +975,8 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust
-    /// #[no_mangle]
-    /// fn foo<T>(t: T) {
-    ///
-    /// }
+    /// #[unsafe(no_mangle)]
+    /// fn foo<T>(t: T) {}
     /// ```
     ///
     /// {{produces}}

compiler/rustc_lint/src/foreign_modules.rs

@@ -35,12 +35,12 @@ declare_lint! {
     ///
     /// ```rust
     /// mod m {
-    ///     extern "C" {
+    ///     unsafe extern "C" {
     ///         fn foo();
     ///     }
     /// }
     ///
-    /// extern "C" {
+    /// unsafe extern "C" {
     ///     fn foo(_: u32);
     /// }
     /// ```

compiler/rustc_lint/src/types.rs

@@ -696,7 +696,7 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust
-    /// extern "C" {
+    /// unsafe extern "C" {
     ///     static STATIC: String;
     /// }
     /// ```