Switch strategies for how rustc's workspace is unioned
Switch strategies for how rustc's workspace is unioned

See rust-lang/rust#52919 for more details.

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