message: Use CMake install directories instead of hardcoded
diff: @@ -239,15 +239,16 @@ if(FLATBUFFERS_BUILD_GRPCTEST)
  endif()
  if(FLATBUFFERS_INSTALL)
  - install(DIRECTORY include/flatbuffers DESTINATION include)
  + include(GNUInstallDirs)
  + install(DIRECTORY include/flatbuffers DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
  if(FLATBUFFERS_BUILD_FLATLIB)
  - install(TARGETS flatbuffers DESTINATION lib)
  + install(TARGETS flatbuffers DESTINATION ${CMAKE_INSTALL_LIBDIR})
  endif()
  if(FLATBUFFERS_BUILD_FLATC)
  - install(TARGETS flatc DESTINATION bin)
  + install(TARGETS flatc DESTINATION ${CMAKE_INSTALL_BINDIR})
  endif()
  if(FLATBUFFERS_BUILD_SHAREDLIB)
  - install(TARGETS flatbuffers_shared DESTINATION lib)
  + install(TARGETS flatbuffers_shared DESTINATION ${CMAKE_INSTALL_LIBDIR})
  endif()
  endif()
  