Merge github.com:grpc/grpc into epex4

Makefile

bazel/cc_grpc_library.bzl

bazel/generate_cc.bzl

bazel/grpc_build_system.bzl

build.yaml

include/grpc++/test/mock_stream.h

src/compiler/cpp_generator.cc

src/compiler/cpp_generator.h

src/compiler/cpp_plugin.cc

src/core/lib/iomgr/udp_server.c

src/proto/grpc/testing/BUILD

src/proto/grpc/testing/compiler_test.proto

templates/Makefile.template

...ols/run_tests/generated/sources_and_headers.json.template

test/core/util/test_config.c

test/cpp/codegen/BUILD

test/cpp/codegen/compiler_test_golden

test/cpp/codegen/compiler_test_mock_golden

test/cpp/codegen/golden_file_test.cc

test/cpp/end2end/mock_test.cc