message: build: fix Makefile build when no BAZEL_CONFIG passed in
diff: -PREFIX = /usr
  -
  -BAZEL_CONFIG = ''
  +# Copyright 2020 The Mesh Authors. All rights reserved.
  +# Use of this source code is governed by the Apache License,
  +# Version 2.0, that can be found in the LICENSE file.
  -LIB_SUFFIX = ''
  +PREFIX = /usr
  +BAZEL_CONFIG =
  +LIB_SUFFIX =
  UNAME_S = $(shell uname -s)
  ifeq ($(UNAME_S),Darwin)
  