zephyr-env.sh: Use $XDG_CONFIG_HOME/zephry/zephyrrc if present

According to the [XDG Base Directory Specification] there is a single base
directory in which user configuration files should be stored. This helps
users to keep their home directory uncluttered. This base directory can be
set in the environment variable $XDG_CONFIG_HOME and defaults to
${HOME}/.config if $XDG_CONFIG_HOME is not set.

This commit adjusts the zephyr-env.sh script to look for a user
configuration file in the following locations:

- $XDG_CONFIG_HOME/zephyr/zephyrrc
- $HOME/.config/zephyr/zephyrrc
- $HOME/.zephyrrc

The first one that is found will be used.

[XDG Base Directory Specification]: (https://specifications.freedesktop.org/basedir-spec/latest/)

Signed-off-by: Andreas Schuster <andreas.schuster@schuam.de>

zephyr-env.sh

@@ -64,6 +64,14 @@ zephyr_answer_file=~/zephyr-env_install.bash
 	. ${zephyr_answer_file}
 }
 unset zephyr_answer_file
-zephyr_answer_file=~/.zephyrrc
-[ -f ${zephyr_answer_file} ] &&  . ${zephyr_answer_file}
-unset zephyr_answer_file
+xdg_config_home="${XDG_CONFIG_HOME:-${HOME}/.config}"
+zephyr_xdg_rc="${xdg_config_home}/zephyr/zephyrrc"
+if [ -f "${zephyr_xdg_rc}" ]; then
+    . "${zephyr_xdg_rc}"
+else
+    zephyr_answer_file=~/.zephyrrc
+    [ -f "${zephyr_answer_file}" ] && . "${zephyr_answer_file}"
+    unset zephyr_answer_file
+fi
+unset zephyr_xdg_rc
+unset xdg_config_home