Fix CMakeLists.txt.

Update dependencies repos versions. Set them as cache variable so one can update them without modifying the cmakelists Add a link between hdbpp-es and libhdbpp, and the proper cmake policy to be able to do this.

it is a follow-up on this issue on the forum: https://www.tango-controls.org/community/forum/c/general/installation/build-hdbpp-mysql-project-mysqlclient-error/