Remove properly tracked config file from .gitignore & add support for skipping of link-checking (#2023)

* Remove properly tracked config file from .gitignore

The file is part of the git history and is a configuration file.

Fixes: #2018

* Add  env. variable support

* Refactoring

* Really skip linkcheck if requested

1 files changed, 8 insertions, 3 deletions

diff --git a/src/doc/rustc-dev-guide/README.md b/src/doc/rustc-dev-guide/README.md
index 599de487b81..d32d2386c9e 100644
--- a/src/doc/rustc-dev-guide/README.md
+++ b/src/doc/rustc-dev-guide/README.md
@@ -59,6 +59,10 @@ The build files are found in the `book/html` directory.
 We use `mdbook-linkcheck2` to validate URLs included in our documentation.
 `linkcheck` will be run automatically when you build with the instructions in the section above.
 
+> [!NOTE]
+> The link validation can be skipped by setting the following environment variable:
+> `SKIP_LINKCHECK=1 mdbook ...`
+
 ### Table of Contents
 
 We use `mdbook-toc` to auto-generate TOCs for long sections. You can invoke the preprocessor by
@@ -66,9 +70,10 @@ including the `<!-- toc -->` marker at the place where you want the TOC.
 
 ## How to fix toolstate failures
 
-> **NOTE**: Currently, we do not track the rustc-dev-guide toolstate due to
-[spurious failures](https://github.com/rust-lang/rust/pull/71731),
-but we leave these instructions for when we do it again in the future.
+> [!NOTE]
+> Currently, we do not track the rustc-dev-guide toolstate due to
+> [spurious failures](https://github.com/rust-lang/rust/pull/71731),
+> but we leave these instructions for when we do it again in the future.
 
 1. You will get a ping from the toolstate commit. e.g. https://github.com/rust-lang-nursery/rust-toolstate/commit/8ffa0e4c30ac9ba8546b7046e5c4ccc2b96ebdd4