Merge pull request #7462 from alalek:cpu_multi_target

diff --cc CMakeLists.txt
Simple merge

diff --cc cmake/OpenCVPCHSupport.cmake
Simple merge

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

diff --cc modules/core/include/opencv2/core/fast_math.hpp
Simple merge

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

diff --cc modules/highgui/CMakeLists.txt
Simple merge

diff --cc modules/imgproc/src/imgwarp.cpp
Simple merge