Merge remote-tracking branch 'upstream/3.4' into merge-3.4

diff --cc CMakeLists.txt
Simple merge

diff --cc cmake/OpenCVDetectCXXCompiler.cmake
Simple merge

diff --cc cmake/OpenCVGenConfig.cmake
Simple merge

diff --cc cmake/OpenCVInstallLayout.cmake
Simple merge

diff --cc modules/calib3d/src/undistort.simd.hpp
Simple merge

diff --cc modules/calib3d/test/test_cameracalibration.cpp
Simple merge

diff --cc modules/calib3d/test/test_undistort.cpp
Simple merge

diff --cc modules/core/include/opencv2/core/cvdef.h
Simple merge

diff --cc modules/core/src/arithm.simd.hpp
Simple merge

diff --cc modules/core/src/parallel_impl.cpp
Simple merge

diff --cc modules/core/src/system.cpp
Simple merge

diff --cc modules/videoio/src/cap_avfoundation_mac.mm
Simple merge