Rollup merge of #125648 - lqd:rustsrc, r=pietroalbini

Remove unused(?) `~/rustsrc` folder from docker script

Every time I run a docker image, the script creates an empty `~/rustsrc` folder. It doesn't seem to be referenced anywhere else, so I'd like to remove it.

Incidentally, this also documents DIST_TRY_BUILD as I fail to find it from a simple search any time I look for it to eg enable tests on try builds.

src/ci/docker/run.sh

@@ -270,7 +270,6 @@ else
   args="$args --volume $root_dir:/checkout$SRC_MOUNT_OPTION"
   args="$args --volume $objdir:/checkout/obj"
   args="$args --volume $HOME/.cargo:/cargo"
-  args="$args --volume $HOME/rustsrc:$HOME/rustsrc"
   args="$args --volume /tmp/toolstate:/tmp/toolstate"
 
   id=$(id -u)

src/ci/github-actions/jobs.yml

@@ -61,6 +61,12 @@ envs:
 
   try:
     <<: *production
+    # The following env var activates faster `try` builds in `opt-dist` by, e.g.
+    # - building only the more commonly useful components (we rarely need e.g. rust-docs in try
+    #   builds)
+    # - not running `opt-dist`'s post-optimization smoke tests on the resulting toolchain
+    #
+    # If you *want* these to happen however, temporarily uncomment it before triggering a try build.
     DIST_TRY_BUILD: 1
 
   auto: