The "Debugging support in the Rust compiler" chapter seems relevant for users rather than contributors

[JohnTitor]

Originally posted by @rylev in #1406 (review):

This also seems correct though some of the information provided seems more relevant for users of Rust rather than those working on the Rust compiler.

Should we move this chapter somewhere or clarify how it's involved in hacking rustc?

[chenyukang]

Sounds great!

For deugging rustc we already has:
https://rustc-dev-guide.rust-lang.org/compiler-debugging.html#configuring-the-compiler

I want to debug rustc with GDB, and can not find enough information on it.
So I spent some time to make it work.
Issues comes from an old GDB version, rust-lang/rust#60705 (comment).

I will try to make a PR to complement it.