cmake HAVE_CXX_FILESYSTEM examples

aljen/spaghetti cmake/DetectCxxFilesystem.cmake :15 

try_compile(HAVE_CXX_FILESYSTEM
  ${CMAKE_CURRENT_BINARY_DIR}/CMakeTemp/HaveCxxFilesystem
  ${CMAKE_CURRENT_BINARY_DIR}/CMakeTemp/test_cxx_filesystem.cc
  CXX_STANDARD 17
  CXX_STANDARD_REQUIRED ON
  OUTPUT_VARIABLE OUTPUT
)

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

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

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 )