Prosed feature: Automatically search Qt6 moc from /usr/lib/qt6/libexec
Prosed feature: Automatically search Qt6 moc from /usr/lib/qt6/libexec
osdn #43331: Targeted to freeciv-3.1: When building against Qt6, automatically search 'moc' also under /usr/lib/qt6/libexec/. At least Debian experimental Qt6 packages install it there, and our current search does not detect it. I think this path is "standard" enough to be one of the paths to search from (for more exotic paths user should set MOCCMD manually)