Fix building against exiv2-0.27
Summary:
Copied FindLibExiv2.cmake from ECM 5.53.0 until we raise min version.
Thanks-to: Boudewijn Rempt <boud@valdyas.org>
for final fix to kis_xmp_io.cpp.
CCBUG: 402566
Test Plan: Built fine against exiv2-0.26 and exiv2-0.27.
Reviewers: Krita, rempt
Reviewed By: Krita, rempt
Subscribers: pino
Tags: Krita
Differential Revision: https://phabricator.kde.org/D17810