Fix building on OpenBSD

FAILED: lib/libopencv_core.so.13.0
...
ld: error: undefined symbol: __cxa_atexit

Do not try to use --no-undefined on OpenBSD. OpenBSD does not link
shared libraries with libc and thus linkage with --no-undefined is
expected to fail.

cmake/OpenCVCompilerOptions.cmake

@@ -391,7 +391,7 @@ endif()
 
 # Apply "-Wl,--no-undefined" linker flags: https://github.com/opencv/opencv/pull/21347
 if(NOT OPENCV_SKIP_LINK_NO_UNDEFINED)
-  if(UNIX AND (NOT APPLE OR NOT CMAKE_VERSION VERSION_LESS "3.2"))
+  if(UNIX AND ((NOT APPLE OR NOT CMAKE_VERSION VERSION_LESS "3.2") AND NOT CMAKE_SYSTEM_NAME MATCHES "OpenBSD"))
     set(_option "-Wl,--no-undefined")
     set(_saved_CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS}")
     set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${_option}")  # requires CMake 3.2+ and CMP0056