Unbreak build with gperf < 3.1
Found by breakage on binary factory for macOS -> https://binary-factory.kde.org/view/MacOS/job/KDiff3_Nightly_macos/lastFailedBuild/console
Related bug report: http://savannah.gnu.org/bugs/?53028
Follow-up work would be to extend FindGperf of ECM to allow version check (edit: now up as extra-cmake-modules!164 (merged)). Then decide on options:
- making 3.1 a min requirement in future KF versions (-> extra-cmake-modules!164 (merged))
- separate kcharset.cpp out into code that is build with the old flag
- provide a custom copy of the generated file
- sed-out the register from the generated file (just kidding)
@dfaure Candidate for 5.84.1 ? See https://repology.org/project/gperf/badges for platforms not yet having 3.1
Edited by Friedrich W. H. Kossebau