cmake HAVE_FLAG examples

vengi-voxel/vengi cmake/system/linux.cmake :53 

check_c_compiler_flag(${_FLAG} HAVE_FLAG${_NAME})

vengi-voxel/vengi cmake/system/linux.cmake :66 

check_c_compiler_flag(${_FLAG} HAVE_FLAG${_NAME})

vengi-voxel/vengi cmake/system/linux.cmake :76 

check_c_compiler_flag(${_FLAG} HAVE_FLAG${_NAME})