Use readelf to find project dependencies

Summary:
We were using a link.txt file that cmake used to generate, on newer cmake
versions it doesn't anymore.
Instead use readelf, much like androiddeployqt does, to extract the
depenencies.
Catch: It relies on having all the binaries being at the same subdirectory,
which is the default in ECM since not long ago.

Test Plan: Build kirigamigallery with it

Reviewers: Frameworks, Build System, aacid

Reviewed By: aacid

Subscribers: mart

Tags: Frameworks, Build System

Differential Revision: https://phabricator.kde.org/D8173