Cherry-picks for the v1.2 branch (future 1.2.1)

Note: mingw32 builds will likely fail until !47 (merged) is merged and also cherry-picked.

I cherry-picked what seemed sensible from MRs merged in master since the 1.2 release. Review welcome to make sure that those don't risk introducing regressions in the stable branch. The aim is to release 1.2.1 as a maintenance update, mostly for convenience of distro packagers to have compiler issues handled (+ some actual engine/game bugfixes).