Akonadi Contact library: Targets not properly exported

[Ben Cooksley]

Hi PIM developers,

It would appear the Akonadi Contact library does not properly export
it's targets, or does so in a manner in which valid include paths for
Akonadi libraries are not included in this.

Could someone please take a look?

This causes Digikam to fail to build on the CI system, please see
https://build.kde.org/view/FAILED/job/digikam%20master%20kf5-qt5/6/PLATFORM=Linux,compiler=gcc/console

Thanks,
Ben