Rollup merge of #58288 - taiki-e:rustc-workspace-hack-2018, r=alexcrichton
Rollup merge of #58288 - taiki-e:rustc-workspace-hack-2018, r=alexcrichton

rustc-workspace-hack => 2018

Transitions `rustc-workspace-hack` to Rust 2018; cc #58099

r? @alexcrichton

aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust