Rollup merge of #144435 - tshepang:rdg-sync, r=jieyouxu

rustc-dev-guide subtree update

Subtree update of `rustc-dev-guide` to https://github.com/rust-lang/rustc-dev-guide/commit/4e310882ba9eaa71a192870837e949854057b3b0.

Created using https://github.com/rust-lang/josh-sync.

r? ```@ghost```

src/doc/rustc-dev-guide/rust-version

@@ -1 +1 @@
-460259d14de0274b97b8801e08cb2fe5f16fdac5
+efd420c770bb179537c01063e98cb6990c439654

src/doc/rustc-dev-guide/src/external-repos.md

@@ -40,27 +40,24 @@ implement a new tool feature or test, that should happen in one collective rustc
     * `portable-simd` ([sync script](https://github.com/rust-lang/portable-simd/blob/master/subtree-sync.sh))
     * `rustfmt`
     * `rustc_codegen_cranelift` ([sync script](https://github.com/rust-lang/rustc_codegen_cranelift/blob/113af154d459e41b3dc2c5d7d878e3d3a8f33c69/scripts/rustup.sh#L7))
-* Using the [josh] tool
-    * `miri` ([sync guide](https://github.com/rust-lang/miri/blob/master/CONTRIBUTING.md#advanced-topic-syncing-with-the-rustc-repo))
-    * `rust-analyzer` ([sync script](https://github.com/rust-lang/rust-analyzer/blob/2e13684be123eca7181aa48e043e185d8044a84a/xtask/src/release.rs#L147))
-    * `rustc-dev-guide` ([josh sync](#synchronizing-a-josh-subtree))
-    * `compiler-builtins` ([josh sync](#synchronizing-a-josh-subtree))
-    * `stdarch` ([josh sync](#synchronizing-a-josh-subtree))
+* Using the [josh](#synchronizing-a-josh-subtree) tool
+    * `miri`
+    * `rust-analyzer`
+    * `rustc-dev-guide`
+    * `compiler-builtins`
+    * `stdarch`
 
 ### Josh subtrees
 
-The [josh] tool is an alternative to git subtrees, which manages git history in a different way and scales better to larger repositories. Specific tooling is required to work with josh; you can check out the `miri` or `rust-analyzer` scripts linked above for inspiration. We provide a helper [`rustc-josh-sync`][josh-sync] tool to help with the synchronization, described [below](#synchronizing-a-josh-subtree).
+The [josh] tool is an alternative to git subtrees, which manages git history in a different way and scales better to larger repositories. Specific tooling is required to work with josh. We provide a helper [`rustc-josh-sync`][josh-sync] tool to help with the synchronization, described [below](#synchronizing-a-josh-subtree).
 
 ### Synchronizing a Josh subtree
 
 We use a dedicated tool called [`rustc-josh-sync`][josh-sync] for performing Josh subtree updates.
-Currently, we are migrating Josh repositories to it. So far, it is used in:
+The commands below can be used for all our Josh subtrees, although note that `miri`
+requires you to perform some [additional steps](https://github.com/rust-lang/miri/blob/master/CONTRIBUTING.md#advanced-topic-syncing-with-the-rustc-repo) during pulls.
 
-- compiler-builtins
-- rustc-dev-guide
-- stdarch
-
-To install the tool:
+You can install the tool using the following command:
 ```
 cargo install --locked --git https://github.com/rust-lang/josh-sync
 ```
@@ -80,6 +77,9 @@ switch to its repository checkout directory in your terminal).
 
 #### Performing push
 
+> NOTE:
+> Before you proceed, look at some guidance related to Git [on josh-sync README].
+
 1) Run the push command to create a branch named `<branch-name>` in a `rustc` fork under the `<gh-username>` account
     ```
     rustc-josh-sync push <branch-name> <gh-username>
@@ -173,3 +173,4 @@ the week leading up to the beta cut.
 [Toolstate chapter]: https://forge.rust-lang.org/infra/toolstate.html
 [josh]: https://josh-project.github.io/josh/intro.html
 [josh-sync]: https://github.com/rust-lang/josh-sync
+[on josh-sync README]: https://github.com/rust-lang/josh-sync#git-peculiarities