Making bootstrap great again

[Shourya742]

High-level issue list to work on bootstrap:

• Refactor all config-related methods (only one's used invoked during parsing) to be independent of specific config states.
• Glue up the config monolith to eliminate fragile invariants scattered across distributed methods.
• Prevent tests from running at the repository root (wording might need adjustment). Self contained. dist_all_cross, and check why its slow. Understand why it is so slow. Try to use profiling tools as well, chrome tracing outputs. Recursive copy or files might be taking time, have some tracing to get to know about blank spaces.
• Align the LLVM step with how the GCC step is handled.
• Investigate the use of Builder::compiler_for, which currently performs some non-obvious behavior.
• Improve command output readability—either by logging to a file or printing in a structured, hierarchical format that integrates well with the step-level debug output.
• Update the bootstrap documentation in rust-dev-guide
• Have look at rustc doc step

@Kobzol, addition of more issue's will be helpful.