don't glob everything and the kitchen sink

Summary:
we have two themes. glob the two themes and nothing else.

otherwise when keeping the build directory in ./build/ we'd glob that too
which may take ages and is entirely useless.

Test Plan: cmake .. && make && cmake .. doesn't take a million years

Reviewers: Breeze, VDG, ngraham

Reviewed By: Breeze, VDG, ngraham

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D21100