Add support for global argument substition list

Make it possible to define arg substitution lists 'globally' per file
so one does not need to redefine same arg substitutions for each build
job.

Change-Id: I71992acf47c1ae05e95fc7ba565f1dcf57e8f0eb
Reviewed-by: Antti Kokko <antti.kokko@digia.com>