Automatically try also moc named 'moc-qt5'/'moc-qt6'
We already support moc-qt5/moc-qt6 when user gives it as MOCCMD, but there's no attempt to find moc by that name if user has not given it. Earlier we've seen such naming only in cygwin, but now I've encountered it also in Manjaro linux while testing Qt6 support there, and it would make things much easier if it was automatically detected.
This ticket is followed by INSTALL.Cygwin update ticket: #41676
Not sure about the S3_1 implementation yet. It probably waits that Qt6 bootstrap gets pushed there too first, and then it can use the patch currently labeled for master only.
Pushed to branches other than S3_1 (which is waiting for the Qt6 bootstrap patch first)