set option to expand aliases

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
diff --git a/op-build-env b/op-build-env
index 9f2bfd2..81cf898 100755
--- a/op-build-env
+++ b/op-build-env
@@ -8,4 +8,5 @@
 export BR2_EXTERNAL=${__PWD}/openpower
 export BR2_DL_DIR=${__PWD}/dl
 
+shopt -s expand_aliases
 alias op-build="make --directory=${__PWD}/buildroot O=${__PWD}/output "