Rollup merge of #84436 - jyn514:private, r=petrochenkov
Rollup merge of #84436 - jyn514:private, r=petrochenkov

Make a few functions private

These were made public in 3105bcfdc11030abf9855af7a693cbf904460813. This
is so long ago I doubt anyone remembers why they're public. No one outside rustc_session uses
them, including in-tree tools.

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