Rollup merge of #78687 - jyn514:bootstrap-help, r=Mark-Simulacrum
Rollup merge of #78687 - jyn514:bootstrap-help, r=Mark-Simulacrum

Suggest library/std when running all stage 0 tests

r? ``@Mark-Simulacrum``
cc ``@ijackson``

For context, this came out of a discord conversation where ``@ijackson`` was running `test --stage 1` when they were only adding doc-tests to the standard library.

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