Feature: Build pure go_binary targets without cc toolchain

[sallustfire]

What version of rules_go are you using?

v0.50.1

What version of Bazel are you using?

7.3.2

Does this issue reproduce with the latest releases of all the above?

Yes

What operating system and processor architecture are you using?

PopOS 22.04

What did you do?

go_binary targets with pure = "on" still participate in cc toolchain selection. This can be seen in one of the examples in the repo:

bazel cquery "somepath(//tests/core/go_binary:static_pure_bin, kind(toolchain, deps(//tests/core/go_binary:static_pure_bin)))"
INFO: Analyzed target //tests/core/go_binary:static_pure_bin (1 packages loaded, 14 targets configured).
INFO: Found 1 target...
//tests/core/go_binary:static_pure_bin (5c86453)
//:go_context_data (55832f6)
//:stdlib (c5fe2ab)
//:cgo_context_data (c5fe2ab)
@bazel_tools//tools/cpp:optional_current_cc_toolchain (c5fe2ab)
INFO: Elapsed time: 0.122s, Critical Path: 0.00s
INFO: 0 processes.
INFO: Build completed successfully, 0 total actions

This happens because //:go_context_data has a dependency on //:cgo_context_data. There are two other places where this same cgo dependency enters //:stdlib and //:cgo_context_data_proxy.

What did you expect to see?

Only the go SDK should be selected

bazel cquery "somepath(//tests/core/go_binary:static_pure_bin, kind(toolchain, deps(//tests/core/go_binary:static_pure_bin)))"
INFO: Analyzed target //tests/core/go_binary:static_pure_bin (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
//tests/core/go_binary:static_pure_bin (5c86453)
@go_sdk//:go_linux_amd64-impl (5c86453)
INFO: Elapsed time: 0.126s, Critical Path: 0.00s
INFO: 0 processes.
INFO: Build completed successfully, 0 total actions

[aaomidi]

I think based on #4154, this might still be an issue.