Add E0619 error explanation

src/librustc_typeck/check/intrinsic.rs

@@ -37,7 +37,7 @@ fn equate_intrinsic_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     match it.node {
         hir::ForeignItemFn(..) => {}
         _ => {
-            struct_span_err!(tcx.sess, it.span, E0619,
+            struct_span_err!(tcx.sess, it.span, E0622,
                              "intrinsic must be a function")
                 .span_label(it.span, "expected a function")
                 .emit();

src/librustc_typeck/diagnostics.rs

@@ -4726,6 +4726,26 @@ let x = &[1_usize, 2] as &[usize]; // ok!
 ```
 "##,
 
+E0622: r##"
+An intrinsic was declared without being a function.
+
+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
+}
+
+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.
+"##,
+
 }
 
 register_diagnostics! {

src/test/compile-fail/E0619.rs

@@ -16,3 +16,4 @@ fn main() {
         _ => {}
     }
 }
+

src/test/compile-fail/invalid-intrinsic.rs → src/test/compile-fail/E0622.rs

@@ -11,6 +11,6 @@
 #![feature(intrinsics)]
 extern "rust-intrinsic" {
     pub static breakpoint : unsafe extern "rust-intrinsic" fn();
-    //~^ ERROR intrinsic must be a function
+    //~^ ERROR intrinsic must be a function [E0622]
 }
 fn main() { unsafe { breakpoint(); } }