poky-init-build-env: unbork for zsh

(From OE-Core rev: 3ef80db73c69b8a731beb8ea4921357a041564e5)

Signed-off-by: Chris Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

poky-init-build-env

@@ -25,7 +25,7 @@
 # being sourced.   To workaround the shell limitation use "set arg1" prior 
 # to sourcing this script.
 #
-if [ "x$0" = "x./poky-init-build-env" ]; then
+if [ -z "$ZSH_NAME" ] && [ "x$0" = "x./poky-init-build-env" ]; then
    echo "Error: This script needs to be sourced. Please run as '. ./poky-init-build-env'"
 else
    if [ -n "$BASH_SOURCE" ]; then