do_build.sh: initialize variables

Initialize some undefined variables identified by set -u.  Future
work: document original feature purpose, current relevance and whether
to remove or test/fix.

OXT-1736

Signed-off-by: Rich Persaud <rich.persaud@baesystems.com>

Author: Rich Persaud

do_build.sh

@@ -41,6 +41,15 @@ BRANCH=master
 BUILD_UID=`id -u`
 export BUILD_UID
 
+DEBUG=""
+CONFIG=""
+XC_TOOLS_BUILD=""
+ARGNAME=""
+OE_BUILD_CACHE_DL=""
+OE_TARBALL_MIRROR=""
+NETBOOT_HTTP_URL=""
+FREEZE_URIS=""
+
 CONF_LOCAL="conf/local.conf"
 
 # TODO: move some of the above definitions into common-config