System information (version)

• OpenCV => 3.4.15
• Operating System / Platform => NetBSD
• Compiler => Clang/GCC

Detailed description

Steps to reproduce

Building fails on NetBSD.
Patch to fix the issue

--- modules/core/src/parallel.cpp.orig  2021-10-06 20:27:21.320272155 +0000
+++ modules/core/src/parallel.cpp
@@ -55,7 +55,7 @@
 
 #if defined __linux__ || defined __APPLE__ || defined __GLIBC__ \
     || defined __HAIKU__ || defined __EMSCRIPTEN__ || defined __FreeBSD__ \
-    || defined __OpenBSD__
+    || defined __OpenBSD__ || defined __NetBSD__
     #include <unistd.h>
     #include <stdio.h>
     #include <sys/types.h>

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  forum.opencv.org, Stack Overflow, etc and have not found solution
• I updated to latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc