zephyr-env.sh: Set correctly $ZEPHYR_BASE in zsh

Sourcing project environment file failed to set correctly
$ZEPHYR_BASE in zsh if it was sourced from another directory
(e.g. home directory). This patch fixes this issue.

It was tested on zsh, bash and sh on Linux.
It needs to be tested on OS X.

Change-Id: Idfb11c6a3109042a9f578f38b3849d9cf9c31f95
Signed-off-by: Yannis Damigos <giannis.damigos@gmail.com>

zephyr-env.sh

@@ -20,6 +20,7 @@
 # sourcing a script. POSIX_ARGZERO option, when it is set, exposes the
 # original value of $0 in spite of the current FUNCTION_ARGZERO setting.
 if [ -n "$ZSH_VERSION" ]; then
+	DIR="${(%):-%N}"
 	if [ $options[posixargzero] != "on" ]; then
 		setopt posixargzero
 		NAME=$(basename -- "$0")
@@ -28,6 +29,7 @@ if [ -n "$ZSH_VERSION" ]; then
 		NAME=$(basename -- "$0")
 	fi
 else
+	DIR="${BASH_SOURCE[0]}"
 	NAME=$(basename -- "$0")
 fi
 
@@ -43,7 +45,7 @@ fi
 uname | grep -q MINGW && MINGW_OPT="-W"
 
 # identify OS source tree root directory
-export ZEPHYR_BASE=$( builtin cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd ${MINGW_OPT})
+export ZEPHYR_BASE=$( builtin cd "$( dirname "$DIR" )" && pwd ${MINGW_OPT})
 
 scripts_path=${ZEPHYR_BASE}/scripts
 echo "${PATH}" | grep -q "${scripts_path}"