message: Add asan, msan, ubsan config options.
  With this change we can use bazel with the different sanitizers more easily with:
  ```
  CC=clang bazel build --config=asan
  CC=clang bazel build --config=msan
  CC=clang bazel build --config=ubsan
  ```
diff: # monolithic: Build all TF C++ code into a single shared object.
  # dynamic_kernels: Try to link all kernels dynamically (experimental).
  # libc++: Link against libc++ instead of stdlibc++
  +# asan: Build with the clang address sanitizer
  +# msan: Build with the clang memory sanitizer
  +# ubsan: Build with the clang undefined behavior sanitizer
  #
  #
  # TF version options;
  @@ -619,3 +622,33 @@ build:release_gpu_linux_cuda_10_1 --config=release_gpu_linux
  build:release_gpu_linux_cuda_10_1 --action_env CUDA_TOOLKIT_PATH="/usr/local/cuda-10.1"
  build:release_gpu_linux_cuda_10_1 --action_env=TF_CUDA_VERSION="10"
  build:release_gpu_linux_cuda_10_1 --action_env=TF_CUDNN_VERSION="7"
  +
  +# Address sanitizer
  +# CC=clang bazel build --config asan
  +build:asan --strip=never
  +build:asan --copt -fsanitize=address
  +build:asan --copt -DADDRESS_SANITIZER
  +build:asan --copt -g
  +build:asan --copt -O3
  +build:asan --copt -fno-omit-frame-pointer
  +build:asan --linkopt -fsanitize=address
  +
  +# Memory sanitizer
  +# CC=clang bazel build --config asan
  +build:msan --strip=never
  +build:msan --copt -fsanitize=memory
  +build:msan --copt -DADDRESS_SANITIZER
  +build:msan --copt -g
  +build:msan --copt -O3
  +build:msan --copt -fno-omit-frame-pointer
  +build:msan --linkopt -fsanitize=memory
  +
  +# Undefined Behavior Sanitizer
  +# CC=clang bazel build --config asan
  +build:ubsan --strip=never
  +build:ubsan --copt -fsanitize=undefined
  +build:ubsan --copt -g
  +build:ubsan --copt -O3
  +build:ubsan --copt -fno-omit-frame-pointer
  +build:ubsan --linkopt -fsanitize=undefined
  +build:ubsan --linkopt -lubsan
  