Filesystem support on OpenBSD

[marcespie]

System information (version)

• OpenCV => 4.5.2
• Operating System / Platform => OpenBSD
• Compiler => clang (not relevant)

Detailed description

The filesystem Impl code is inactive, because there is no set of definitions for OpenBSD.

Steps to reproduce

noticed while porting gmic and trying to use camera.

I have a
patch.txt
patch to fix this, it's really as stupid as adding OpenBSD where FreeBSD is mentioned, and gmic camera now works.

[alalek]

Thank you for the report!

Fell free to create PR with required changes.
Prefer to keep __FreeBSD__ and __OpenBSD__ checks on the same code line.

[marcespie]

I don't have the git source of opencv around, so if some frequent developer would apply the patch and actually fix that, that would be swell.