libobs/util: Reject plugins linking Qt5 library for Linux

Since obs-studio switched to Qt6, old plugins linking Qt5 should be
rejected. On Linux system, OBS and it's plugins link the system
libraries so that obs could be crashed by such plugins that links Qt5
when Qt5 functions are called.

Co-authored-by: Norihiro Kamae <norihiro@nagater.net>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f