move version definition into generated header instead of passing it on CLI

Summary:
easier to for IDEs to follow where it comes from and also more in line
with how other defines are set in drkonqi

Test Plan: builds

Reviewers: jriddell, apol

Reviewed By: apol

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D19543