This avoids conflicting names in a couple of cases.
1. Within google, we want to sync files but not name them BUILD (since the structure doesn't match).
2. On case-insensitive filesystems, `build` may be used for a build directory. Naming `BUILD.bazel` avoids potentioal conflicts.
This change adds `rules_pkg`-based targets that will produce source distribution archives, similar to `make dist`.
These rules produce nearly the same outputs as `make dist`. However, there are some differences and caveats:
1. The outputs do not contain vendored googletest sources.
2. You have to run `autogen.sh` before `blaze build pkg:all`. This produces several autotools-related files directly into the source tree.
3. The output .zip files do not have a directory prefix like `protobuf-3.20.1-rc-1` (this will be addressed after [Substitute package variables in `pkg_zip#package_dir`. bazelbuild/rules_pkg#577](https://github.com/bazelbuild/rules_pkg/pull/577); the tar files do have this prefix, though.)
4. One file is missing from the archives, which is produced during the `make` build: benchmarks/gogo/cpp_no_group/cpp_benchmark.cc
5. In several places, I have explicitly excluded some files that are not in the autotools distribution outputs. I think most of those files should probably be included, but for now, I'm aiming for parity with `make dist`. These are marked with comments, so it should be easy to clean them up later.
This change adds the required loads to examples and zlib.
For full compatibility with --incompatible_load_{cc,java,proto}_rules_from_bzl,
we will need to roll gtest to a newer version.
The example utilizes native bazel rules (proto_library, cc_proto_library,
java_proto_library, java_lite_proto_library) to show how easy it is to
build protobuf with bazel's native support. It also makes use of well
known types which was not possible until the latest bazel 0.5.4 release
and https://github.com/google/protobuf/pull/3594 .