Auto merge of #6176 - oli-obk:patch-1, r=alexcrichton

Future proof an unstable test

statics (even extern ones) will get their type checked for a `Sized` bound in order to fix rust-lang/rust#54410

Author: bors

tests/testsuite/doc.rs

@@ -568,9 +568,12 @@ fn doc_target() {
         .file(
             "src/lib.rs",
             r#"
-            #![feature(no_core)]
+            #![feature(no_core, lang_items)]
             #![no_core]
 
+            #[lang = "sized"]
+            trait Sized {}
+
             extern {
                 pub static A: u32;
             }