Tracking issue for post stage 0 bootstrap sequence redesign follow-ups and bugs

[jieyouxu]

Note

Please open individual issues for individual bugs or problems instead of this tracking issue.

Follow-ups to #119899.
Support thread: #t-infra/bootstrap > Stage 0 std redesign support thread
Internal blog post for quick context: https://blog.rust-lang.org/inside-rust/2025/05/29/redesigning-the-initial-bootstrap-sequence/.

(This issue should be unpinned by the next release cycle)

[jyn514]

cc:

• bootstrap blog post should document how x check has changed and what to do instead #142051
• stage1 compiler has some debuginfo with misleading library paths #142050
• get rid of stage0-sysroot #142052

download-rustc issues that are not directly related but cause a lot more trouble now:

• bootstrap: Build using download-rustc can modify Cargo.lock for non compiler/ deps, causing rustc to not be downloaded on next build #141986
• bootstrap: force download-rustc=if-unchanged even if settings differ #141953
• download-rustc downloads rustc-dev even when it is not needed #142013