CMakePackageConfigHelpers: Restore undocumented PACKAGE_PREFIX_DIR variable
Revert !9390 (merged). It regressed existing
projects that rely on the undocumented PACKAGE_PREFIX_DIR
variable in
package configuration files generated by CMakePackageConfigHelpers
.
Fixes: #25873 (closed)
Fixes: #25885 (closed)
Issue: #25827 (closed)
Backport: release
Edited by Brad King