Auto merge of #38049 - frewsxcv:libunicode, r=alexcrichton

Rename 'librustc_unicode' crate to 'libstd_unicode'.

Fixes https://github.com/rust-lang/rust/issues/26554.

src/libserialize/lib.rs

@@ -41,7 +41,7 @@ Core encoding and decoding interfaces.
 #[cfg(test)] extern crate test;
 #[macro_use] extern crate log;
 
-extern crate rustc_unicode;
+extern crate std_unicode;
 extern crate collections;
 
 pub use self::serialize::{Decoder, Encoder, Decodable, Encodable};