chore: import upstream snapshot with attribution

modules/core/cmake/parallel/detect_openmp.cmake

@@ -0,0 +1,13 @@
+if(CMAKE_VERSION VERSION_LESS "3.9")
+  message(STATUS "OpenMP detection requires CMake 3.9+")  # OpenMP::OpenMP_CXX target
+endif()
+
+find_package(OpenMP)
+if(OpenMP_FOUND)
+  if(TARGET OpenMP::OpenMP_CXX)
+    set(HAVE_OPENMP 1)
+    ocv_add_external_target(openmp "" "OpenMP::OpenMP_CXX" "HAVE_OPENMP=1")
+  else()
+    message(WARNING "OpenMP: missing OpenMP::OpenMP_CXX target")
+  endif()
+endif()

modules/core/cmake/parallel/detect_tbb.cmake

@@ -0,0 +1,5 @@
+include("${OpenCV_SOURCE_DIR}/cmake/OpenCVDetectTBB.cmake")
+
+if(HAVE_TBB)
+  ocv_add_external_target(tbb "" "tbb" "HAVE_TBB=1")
+endif()

modules/core/cmake/parallel/init.cmake

@@ -0,0 +1,8 @@
+macro(ocv_add_core_parallel_backend backend_id cond_var)
+  if(${cond_var})
+    include("${CMAKE_CURRENT_LIST_DIR}/detect_${backend_id}.cmake")
+  endif()
+endmacro()
+
+ocv_add_core_parallel_backend("tbb" WITH_TBB)
+ocv_add_core_parallel_backend("openmp" WITH_OPENMP)