make darwin_objc docs build for more targets

Author: jbatez

library/core/src/os/mod.rs

@@ -2,6 +2,16 @@
 
 #![unstable(feature = "darwin_objc", issue = "145496")]
 
+#[cfg(all(
+    doc,
+    any(
+        all(target_arch = "wasm32", not(target_os = "wasi")),
+        all(target_vendor = "fortanix", target_env = "sgx")
+    )
+))]
+#[unstable(issue = "none", feature = "std_internals")]
+pub mod darwin {}
+
 // darwin
 #[cfg(not(all(
     doc,

library/std/src/os/darwin/objc.rs

@@ -2,4 +2,7 @@
 
 #![unstable(feature = "darwin_objc", issue = "145496")]
 
-pub use core::os::darwin::objc::{Class, SEL, class, objc_class, objc_selector, selector};
+// The `no_inline`-attribute is required to make the documentation of all targets available.
+// See https://github.com/rust-lang/rust/pull/57808#issuecomment-457390549 for more information.
+#[doc(no_inline)]
+pub use core::os::darwin::objc::*;