lang/rust: Update to 1.27.1

Release notes:

• https://blog.rust-lang.org/2018/06/21/Rust-1.27.html
• https://blog.rust-lang.org/2018/07/10/Rust-1.27.1.html

Rust is marked as broken on aarch64. The reason is the bootstrap
compiler crashes currently. See PR 228892 which tracks the issue.

A patch for aarch64 is still included. It fixes the sign for unqualified
C char. This patch still needs to be upstream, but for that, the
compiler needs to work again first.

PR: 228892