build: allow building without scion-ci

[mlegner]

My motivation for this is an error on ARM64 machines when building scion-ci:

(13:40:17) ERROR: /home/ubuntu/.cache/bazel/_bazel_ubuntu/d590279010957ac1dca373a0e19d0c3c/external/io_bazel_rules_go/BUILD.bazel:86:17: While resolving toolchains for target @io_bazel_rules_go//:cgo_context_data: No matching toolchains found for types @bazel_tools//tools/cpp:toolchain_type.

However, it may be interesting irrespective of this to just build the main binaries without the CI tools.

Maybe the naming could be improved, let me know what you think.

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This change is 

[matzf]

Thanks!

For context: the error occurs because building some of the tools requires cgo. Specifically, this is braccept which uses the cgo-based gopacket/afpacket library to write raw packets.
As I see it, the braccept utility is solely built used for the router_multi test, which is triggered from within bazel, and does not need the output of the scion-ci target. As an alternative approach, I think it could make sense to just drop braccept from the scion-ci target.

If we decide to go for the approach with different make targets, I think it could make sense to call the non-ci variant just something plain like build, and the variant with the CI tools something like build-dev.
Or, something like dist-bin could make sense for the no-CI variant; I was planning to add a make target dist-deb for building debian packages (see WIP #4448), so this could also fit.

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[jiceatscion]

gopacket is also used by brload now.

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[mlegner]

If we decide to go for the approach with different make targets, I think it could make sense to call the non-ci variant just something plain like build, and the variant with the CI tools something like build-dev.
Or, something like dist-bin could make sense for the no-CI variant; I was planning to add a make target dist-deb for building debian packages (see WIP #4448), so this could also fit.

All of these sound fine to me, no strong preference either way. I'm happy to update this PR, but feel free to just close it and include this in a separate PR.

[matzf]

Ok. Let's just add the make target that you propose then.
My preference for the name would be something like dist, dist-bin, or build (and build-dev for the "ci" variant) -- nothing with "bazel".
Please mark the target as .PHONY.

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[mlegner]

@matzf How about this version with build and build-dev and build-dev as the default target?

[matzf]

💯

Reviewed 3 of 3 files at r2, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @mlegner)

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doc/dev/setup.rst line 75 at r2 (raw file):

      make

  .. hint:: This installs tools for tests in addition to the main SCION services (e.g., `end2end`);

Nit: I think "installs" could be mistaken here, just "build" or "compile" might be better.

[matzf]

Reviewed 1 of 1 files at r3, all commit messages.
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