Clean up E0622 explanation

src/librustc_error_codes/error_codes/E0622.md

@@ -5,13 +5,21 @@ Erroneous code example:
 ```compile_fail,E0622
 #![feature(intrinsics)]
 extern "rust-intrinsic" {
-    pub static breakpoint : unsafe extern "rust-intrinsic" fn();
-    // error: intrinsic must be a function
+    pub static breakpoint : fn(); // error: intrinsic must be a function
 }
 
 fn main() { unsafe { breakpoint(); } }
 ```
 
 An intrinsic is a function available for use in a given programming language
 whose implementation is handled specially by the compiler. In order to fix this
-error, just declare a function.
+error, just declare a function. Example:
+
+```no_run
+#![feature(intrinsics)]
+extern "rust-intrinsic" {
+    pub fn breakpoint(); // ok!
+}
+
+fn main() { unsafe { breakpoint(); } }
+```