Make it possible for IBuildSystem to provide extra arguments to the parser
Summary:
So far it was limited to defines and includes, but there's more to life
than that.
This implements it for cmake where I tested it most, also for qmake where
I'm not sure how to yet it won't be worse than ignoring the variables.
Reviewers: KDevelop, kfunk
Subscribers: kdevelop-devel
Differential Revision: https://phabricator.kde.org/D7752