Base.GIT_VERSION_INFO: record the Buildkite commit that was used to…

… build Julia (#43073)

(cherry picked from commit a21cc80)

base/version_git.sh

@@ -13,6 +13,8 @@ echo "    date_string::AbstractString"
 echo "    tagged_commit::Bool"
 echo "    fork_master_distance::Int"
 echo "    fork_master_timestamp::Float64"
+echo "    build_system_commit::String"
+echo "    build_system_commit_short::String"
 echo "end"
 echo ""
 
@@ -82,6 +84,16 @@ if [ -z "$fork_master_timestamp" ]; then
     fork_master_timestamp="0"
 fi
 
+build_system_directory="../.buildkite"
+if [[ -d "${build_system_directory}/.git" ]]; then
+    build_system_commit=$(git -C "${build_system_directory}" rev-parse HEAD)
+    build_system_commit_short=$(git -C "${build_system_directory}" rev-parse --short HEAD)
+else
+    echo "Warning: The build system directory does not exist or is not a Git repo: ${build_system_directory}" >&2
+    build_system_commit=""
+    build_system_commit_short=""
+fi
+
 echo "const GIT_VERSION_INFO = GitVersionInfo("
 echo "    \"$commit\","
 echo "    \"$commit_short\","
@@ -90,5 +102,7 @@ echo "    $build_number,"
 echo "    \"$date_string\","
 echo "    $tagged_commit,"
 echo "    $fork_master_distance,"
-echo "    $fork_master_timestamp."
+echo "    $fork_master_timestamp.,"
+echo "    \"$build_system_commit\","
+echo "    \"$build_system_commit_short\","
 echo ")"