Add platform contraints for GOAMD64

[fmeum]

What type of PR is this?

Feature

What does this PR do? Why is it needed?

The new constraints //go/constraints/amd64:v1 to v4 can be used to
mark a platform as supporting the corresponding level of GOAMD64.

To use the new feature, users would supply their own platform:

platform(
    name = "amd64_with_avx",
    contraint_values = [
        "@platforms//os:linux",
        "@platforms//cpu:x86_64",
        "@io_bazel_rules_go//go/constraints/amd64:v3",
    ],
)

and then specify the platform with --platforms.

Which issues(s) does this PR fix?

Fixes #3248

Other notes for review

[rabbbit]

Thanks for the quick reaction!

Looks very promising (and almost definitely is what I need), I left a note on #3248.

[achew22]

I'd like to see @linzhp run this on the big repo, but LGTM

[fmeum]

@achew22 Do you know a good place in the docs where I could explain this new feature?

[linzhp]

The changes look good to me. @rabbbit Did you test it in Uber?

[rabbbit]

I patched it and can confirm the env contains the variable I need/want.

SUBCOMMAND: # @io_bazel_rules_go//:stdlib [action 'GoStdlib external/io_bazel_rules_go/stdlib_/pkg', configuration: be3be823bbdbc6e9db2eea6ed500a467975e027a0c143a8f63ba4d6e234e927a, execution platform: @local_config_platform//:host]
(cd /private/var/tmp/_bazel_pawel/592aedee41e8f957ae1ee499da1dedeb/execroot/__main__ && \
  exec env - \
    CGO_ENABLED=0 \
    GOAMD64=v3 \
    GOARCH=amd64 \
    GOOS=linux \
    GOPATH='' \
    GOROOT=external/go_sdk \
    GOROOT_FINAL=GOROOT \

I have not tested whether the actual variable has an effect (yet), but this change looks good - thanks for the help @fmeum! :)

[sluongng]

It would be nice if instead of having to use bazel build --platforms=//my/custom/platform:with_avx, user can just specify this under an attribute of go_binary instead (similar to goos and goarch).

[fmeum]

It would be nice if instead of having to use bazel build --platforms=//my/custom/platform:with_avx, user can just specify this under an attribute of go_binary instead (similar to goos and goarch).

We generally want to move away from that approach, but introduce a wrapper rule that transitions to a different user-provided platform. That gives you clear semantics with select and less rebuilds since you are not switching between synthetic platforms.