rollup merge of #23211: FlaPer87/oibit-send-and-friends

Fixes #23225

r? @nikomatsakis

src/test/compile-fail/coherence-default-trait-impl.rs

@@ -21,4 +21,14 @@ impl MyTrait for .. {}
 impl MyTrait for .. {}
 //~^ ERROR conflicting implementations for trait `MyTrait`
 
+trait MySafeTrait: MarkerTrait {}
+
+unsafe impl MySafeTrait for .. {}
+//~^ ERROR implementing the trait `MySafeTrait` is not unsafe
+
+unsafe trait MyUnsafeTrait: MarkerTrait {}
+
+impl MyUnsafeTrait for .. {}
+//~^ ERROR the trait `MyUnsafeTrait` requires an `unsafe impl` declaration
+
 fn main() {}

src/test/run-make/rustdoc-default-impl/foo.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(optin_builtin_traits)]
+
 pub mod bar {
     use std::marker;