In Qt >= 5.12, the qhelpgenerator and qcollectiongenerator tools were fused, only qhelpgenerator remains.

Allow using ECMQueryQmake inside ECM.

Due to project(ECM) specifying the "NONE" language, find_package(Qt5Core)
cannot succeed.

if the Qt5::qmake target doesn't exist, we now look for the qmake executable.

Add FindExiv2.cmake to ECM

According to lxr, we have 8 copies of this module in different repositories (+kdelib4support and a playground repo).