WORKSPACE: Fix Bazel 4 protobuf build error

[tomtseng]

On my macOS machine with Bazel 4.2.1, when I try to build, I get an immediate build error:

ERROR: /private/var/tmp/_bazel_t/12fcc22211704038f32f3c5236102e5e/external/com_google_protobuf/BUILD:979:21: in proto_lang_toolchain rule @com_google_protobuf//:cc_toolchain: '@com_google_protobuf//:cc_toolchain' does not have mandatory provider 'ProtoInfo'.
ERROR: Analysis of target '//clusterers/ldd_clusterer:ldd-clusterer' failed; build aborted: Analysis of target '@com_google_protobuf//:cc_toolchain' failed

Moving the rules_proto section higher in WORKSPACE fixes this issue on my machine.

Building with this change on an Ubuntu 18.04 machine with Bazel 3 still works.

(I still can't build on macOS because of external/gbbs/gbbs/io.cc:20:11: error: use of undeclared identifier ‘M_MMAP_MAX’ but that's a separate issue.)

cc @jeshi96 @yushangdi

[yushangdi]

I have the same problem. For a temporary fix, I commented out line 18-25 in gbbs/io.cc and it worked on my mac. But we should figure out a better fix.