message: Add a new bazel config option for C++ 17
diff: @@ -90,6 +90,12 @@ build --define=grpc_no_ares=true
  build:dynamic_kernels --define=dynamic_loaded_kernels=true
  build:dynamic_kernels --copt=-DAUTOLOAD_DYNAMIC_KERNELS
  +# Build TF with C++ 17 features.
  +build:c++17 --cxxopt=-std=c++1z
  +build:c++17 --cxxopt=-stdlib=libc++
  +build:c++1z --cxxopt=-std=c++1z
  +build:c++1z --cxxopt=-stdlib=libc++
  +
  # Default paths for TF_SYSTEM_LIBS
  build --define=PREFIX=/usr
  build --define=LIBDIR=$(PREFIX)/lib
  