[cmake] fix CXX11 test: on osx CMAKE_CXX_COMPILER_ID is "AppleClang"
[cmake] fix CXX11 test: on osx CMAKE_CXX_COMPILER_ID is "AppleClang"

poparteu/openMVG,poparteu/openMVG,poparteu/openMVG,poparteu/openMVG