Add user archiver flags into C++ toolchains

[Fil-Den]

Closes: #22861.

[keith]

how are these set? I don't see user_archiver_flags referenced anywhere else?

[Fil-Den]

@keith, I can use it by calling create_linking_context_from_compilation_outputs with the variables_extension argument. Code will looks like:

(linking_context, linking_outputs) = cc_common.create_linking_context_from_compilation_outputs(
    name = output_name,
    actions = ctx.actions,
    feature_configuration = feature_configuration,
    cc_toolchain = cc_toolchain,
    language = "c++",
    compilation_outputs = compilation_outputs,
    linking_contexts = [compilation_cc_info.linking_context],
    disallow_dynamic_library = True,
    variables_extension = {
        "user_archiver_flags": user_link_flags
    },
)

[keith]

ah cool. I think the google folks will have to look at this. they might ask for a test here, or a general way for folks to pass this who aren't calling that function directly

[Fil-Den]

@keith, do we wait for someone else to review this PR?

[keith]

Yea probably @pzembrod

[Fil-Den]

@pzembrod, can you take a look at the PR?