cmake HAVE_CXX_FILESYSTEM examples

FluidSynth/fluidsynth CMakeLists.txt :563 

unset ( HAVE_CXX_FILESYSTEM CACHE )

FluidSynth/fluidsynth CMakeLists.txt :567 

check_include_file_cxx ( filesystem HAVE_CXX_FILESYSTEM )

FluidSynth/fluidsynth CMakeLists.txt :570 

endif ( NOT HAVE_CXX_FILESYSTEM )

mariadb-corporation/MaxScale cmake/BuildLibVault.cmake :3 

CHECK_INCLUDE_FILE_CXX(filesystem HAVE_CXX_FILESYSTEM CMAKE_REQUIRED_FLAGS -std=c++17)