rollup merge of #19000: IvanUkhov/doc-link-dylib

Hello,

`dylib` [seems][1] to be no longer an option for the `kind` key of the `link` attribute.

UPDATE: It should be the other way around: It [seems][1] `dylib` has been lost as a possible variant of the `kind` key of the `link` attribute. See the comment below.

Regards,
Ivan

[1]: 8f87538786/src/librustc/metadata/creader.rs (L237)

src/librustc/metadata/creader.rs

@@ -242,6 +242,8 @@ fn visit_item(e: &Env, i: &ast::Item) {
                                     cstore::NativeFramework
                                 } else if k.equiv(&("framework")) {
                                     cstore::NativeFramework
+                                } else if k.equiv(&("dylib")) {
+                                    cstore::NativeUnknown
                                 } else {
                                     e.sess.span_err(m.span,
                                         format!("unknown kind: `{}`",