Don't rebuild rustdoc after checking bootstrap
Don't rebuild rustdoc after checking bootstrap

This works by unconditionally passing -Z unstable-options to the
compiler. This has no affect in practice since bootstrap doesn't use
`deny(rustc::internal)`.

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