Raise c++ compiler baseline

[davido]

Trying to upgrade gRPC to 1.3.8:[1] to fix building Bazel itself on gcc 11 (now default on Fedora Rawhide 34), we are running in this issue: [2]

external/com_google_absl/absl/time/internal/cctz/include/cctz/civil_time_detail.h:26:5: warning: "__cpp_constexpr" is not defined [-Wundef]
 #if __cpp_constexpr >= 201304 || (defined(_MSC_VER) && _MSC_VER >= 1910)
     ^
(20:52:47) ERROR: /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/ec321eb2cc2d0f8f91b676b6d4c66c29/external/com_github_grpc_grpc/BUILD:3481:16: Compiling src/core/ext/upb-generated/google/protobuf/timestamp.upb.c [for host] failed: (Exit 1): gcc failed: error executing command

Looking into the related docker image, gcc is totally outdated:

  $ docker run -it gcr.io/bazel-public/centos7-java8:latest /bin/bash
  $ gcc --version
gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44)
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Raise the baseline and remove outdated toolchains.

Possibly related: [3].

[1] bazelbuild/bazel#13536
[2] https://buildkite.com/bazel/bazel-bazel-github-presubmit/builds/8847#f244407a-e587-456e-9882-1632034dd773
[3] grpc/grpc#26121

[philwo]

@davido We cannot upgrade the gcc compiler on this platform. CentOS 7 ships this version of gcc so we have to deal with it - we are (purposefully) always using and testing with the default toolchains provided by the distributions that we support to ensure that Bazel can be built and works out of the box on these systems.

[davido]

@philwo

We cannot upgrade the gcc compiler on this platform.

Thanks for clarifying. Remove the outdated platforms, then?

But anyway, this could be handled in another issue.

[philwo]

Remove the outdated platforms, then?

I'm always happy if we can remove support for old platforms, because then we can move to more modern tools, reduce infrastructure complexity, etc.

On the other hand we don't want to remove support for something that's still important for our users. :( As we don't have telemetry, it's very difficult to get clear signal on which platforms are still important and which aren't.

Considering that Ubuntu 16.04 LTS is now also EOL, it might be reasonable to drop support for Ubuntu 14.04 / 16.04 / CentOS 7 on Bazel's master branch. Looking forward to discuss - do you want to file an issue to propose this?

[davido]

Looking forward to discuss - do you want to file an issue to propose this?

Done.