When deploying into some directory structure where CMAKE_INSTALL_LIBDIR is different from Qt's lib dir, we need to set the RPATH of installed plugins such that Qt libraries are found. We do this using CMake's undocumented file(RPATH_SET) command and pray that this command is safe to use across current and future CMake versions. For CMake versions < 3.21, we use patchelf, which must be installed on the host system. The adjustment of rpaths can be turned on explicitly by setting QT_DEPLOY_FORCE_ADJUST_RPATHS to ON. The usage of patchelf can be forced by setting QT_DEPLOY_USE_PATCHELF to ON regardless of the CMake version. Change-Id: I62ced496b4c12bf6d46735d2af7ff35130148acb Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>