refactor(bazel): share the platform-independent toolchain config

[Alexandr-Solovev]

Description

Fourth step of the Bazel maintainability series. Addresses the "Toolchain code
unification" item that has been open in dev/bazel/TODO.md since 2023:

There is logic duplication for toolchain configuration on Linux/Windows.

Stacked on #3829 (shares its load() edits); merge that one first.

What is actually duplicated, and what is not

cc_toolchain_config_lnx.bzl and cc_toolchain_config_win.bzl are 2,177 lines
describing two different compiler drivers. Most of that is not duplication: of
the 30 features both files define under the same name, none were textually
identical, because they differ in the flags they emit — -I against /I,
-include against /FI, -MD -MF against /clang:-MD /clang:-MF.

What was duplicated is the part that contains no flag syntax at all:

• the action groups — all_compile_actions, all_cpp_compile_actions,
  all_link_actions, lto_index_actions: plain lists of ACTION_NAMES, byte
  for byte the same in both files;
• ten features and action configs whose flags come entirely from rule
  attributes or from Bazel build variables:
  cpp_link_static_library, supports_dynamic_linker,
  do_not_link_dynamic_dependencies, compiler_input_flags,
  linker_param_file, user_compile_flags, user_link_flags,
  default_link_flags, default_dynamic_libraries and the per-ISA
  <cpu>_flags;
• the 28 rule attributes both cc_toolchain_config rules declare, in the
  same order with the same types.

Those move to cc_toolchain_config_common.bzl. The per-compiler features stay
where they are: a shared factory with a if is_windows branch inside it would
be harder to follow than the duplicate it replaces, and the module docstring
says so, so the next person does not "finish the job" by merging the rest.

preprocessor_compile_actions and codegen_compile_actions were defined in
both files and referenced in neither; they are dropped rather than moved.

410 lines leave the two platform files; 341 arrive in the shared one, about a
third of which is the documentation the originals never had.

Validation

• Every moved block was diffed against both originals after normalising
  whitespace and substituting the factory parameters back to the ctx.attr.*
  expressions they replace — 20 comparisons, all identical.
• bazel build //cpp/daal:core_static //cpp/oneapi/dal/algo:kmeans_dpc after
  the change is a full action-cache hit (1,572 actions, 0 re-executed),
  i.e. not one compile or link command line moved on Linux.
• bazel build --nobuild //:release //:release_all //examples/oneapi/cpp:all
  analyses clean.

Windows is covered by the WindowsBazel jobs on this PR; the shared blocks are
textually identical to what that toolchain used before.

---

• I have reviewed my changes thoroughly before submitting this pull request.
• I have commented my code, particularly hard-to-understand areas.
• I have updated the documentation or contribution guidelines as needed.
• I have added tests that reproduce the issue or verify the new functionality.
• All new and existing tests pass.

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🔵 Needs a closer look

The shared configuration affects both platform toolchains, so cross-platform behavior warrants final human review.

Review effort: Balanced
Findings: None

What changed in this PR

This PR consolidates platform-independent Bazel C++ toolchain configuration while keeping Linux- and Windows-specific compiler flags separate. It also carries cleanup from the preceding PR, #3829.

Changes:

• Moves shared action groups, features, and rule attributes into a common toolchain module.
• Renames the Linux extra-toolchain template and removes unused imports, code, and configuration whitespace.

File	Description
dev/​bazel/​toolchains/​extra_toolchain_lnx.tpl.BUILD	Renamed Linux extra-toolchain template.
dev/​bazel/​toolchains/​extra_toolchain_lnx.bzl	Points to the renamed template.
dev/​bazel/​toolchains/​cc_toolchain_config_win.bzl	Uses shared toolchain definitions.
dev/​bazel/​toolchains/​cc_toolchain_config_lnx.bzl	Uses shared toolchain definitions.
dev/​bazel/​toolchains/​cc_toolchain_config_common.bzl	Defines shared actions, features, and attributes.
dev/​bazel/​release.bzl	Removes an unused toolchain declaration.
dev/​bazel/​cc/​link.bzl	Removes an unused import.
dev/​bazel/​cc/​common.bzl	Removes an unused import.
dev/​bazel/​cc.bzl	Removes an unreachable copy branch and an unused import.
.bazelrc	Removes an empty directive and trailing whitespace.

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[napetrov]

Verified locally: 0 actions re-run vs #3829, release tree byte-identical to base.

[Alexandr-Solovev]

Superseded by #3833, which now carries this PR's commits unchanged (plus the review fixes made here), rebased on current main, together with the rest of the dev/bazel series. Closing to avoid reviewing and merging the same changes twice.