sys-kernel/coreos-sources: Add a script for sorting configs

The script sorts the lines in the config files and prints a messages
when some variable is being overridden (means that it is specified
twice in the config).

The script can be also used to check for such situations with full
configs like:

    cat commonconfig-* amd64_defconfig-* >amd64fullconfig
    ./sort_config.sh amd64fullconfig
    rm amd64fullconfig

sdk_container/src/third_party/coreos-overlay/sys-kernel/coreos-modules/files/sort_config.sh

@@ -0,0 +1,45 @@
+#!/bin/bash
+
+# This script sorts the config files. It can be called with several
+# config files too, so it will sort each file separately.
+
+set -euo pipefail
+
+c_locale_sort()
+{
+    LC_ALL=C sort "${@}"
+}
+
+for cfgfile in "${@}"
+do
+    mapfile -t lines <"${cfgfile}"
+    declare -A variables # a hash map
+    for line in "${lines[@]}"
+    do
+        var="${line%%=*}"
+        var="${var#\# }"
+        var="${var%% *}"
+        if [[ ${variables[${var}]+isset} ]]
+        then
+            echo "${cfgfile}: overriding ${var}"
+        else
+            variables[${var}]=1
+            declare -a "LINES_FOR_${var}"
+        fi
+        declare -n var_lines="LINES_FOR_${var}"
+        var_lines+=("${line}")
+        unset -n var_lines
+    done
+    mapfile -t sorted_variables < <(printf '%s\n' "${!variables[@]}" | c_locale_sort)
+    truncate --size=0 "${cfgfile}"
+    for var in "${sorted_variables[@]}"
+    do
+        declare -n var_lines="LINES_FOR_${var}"
+        printf '%s\n' "${var_lines[@]}" >>"${cfgfile}"
+        unset var_lines
+        unset -n var_lines
+    done
+    unset sorted_variables
+    unset lines
+    unset variables
+done