Backport libs stabilizations to 1.21 beta

This includes the following stabilizations:

- tcpstream_connect_timeout https://github.com/rust-lang/rust/pull/44563
- iterator_for_each https://github.com/rust-lang/rust/pull/44567
- ord_max_min https://github.com/rust-lang/rust/pull/44593
- compiler_fences https://github.com/rust-lang/rust/pull/44595
- needs_drop https://github.com/rust-lang/rust/pull/44639
- vec_splice https://github.com/rust-lang/rust/pull/44640

src/libstd/net/tcp.rs

@@ -167,7 +167,7 @@ impl TcpStream {
     /// connection request.
     ///
     /// [`SocketAddr`]: ../../std/net/enum.SocketAddr.html
-    #[stable(feature = "tcpstream_connect_timeout", since = "1.22.0")]
+    #[stable(feature = "tcpstream_connect_timeout", since = "1.21.0")]
     pub fn connect_timeout(addr: &SocketAddr, timeout: Duration) -> io::Result<TcpStream> {
         net_imp::TcpStream::connect_timeout(addr, timeout).map(TcpStream)
     }