Compile tests files with enabled exceptions, required for exiv2 0.27

Summary: This is a follow up of https://cgit.kde.org/gwenview.git/patch/?id=b81eed1dc4d879f06d651ea0954bee1b46c7947e to also make the tests build withour running into errors when building against exiv2 0.27.

Reviewers: #gwenview, ngraham

Reviewed By: #gwenview, ngraham

Subscribers: ngraham, #gwenview

Tags: #gwenview

Differential Revision: https://phabricator.kde.org/D19169