Use $(python) built-in in Kconfig

[jserv]

This replaces 'tools/kconfig' git submodule with shallow on-demand clone triggered by 'make defconfig' or 'make config'. Add 'make distclean' to remove the cloned Kconfiglib along with build artifacts.

It converts all boolean $(shell,...) checks in configs/Kconfig to the portable $(python,...) preprocessor function, which evaluates Python code in-process without spawning a shell. This eliminates shell-specific idioms (2>/dev/null, && echo y || echo n, test -n) and the shell injection vector from environment variables.

COMPILER_TYPE retains $(shell,...) since $(python,...) only returns y/n and cannot produce string output.

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Summary by cubic

Switch Kconfig to the built-in $(python) function for boolean checks and fetch Kconfiglib via an on-demand shallow clone. This removes shell-specific logic, improves portability, and reduces risk from env-based shell injection; adds distclean for cleanup.

• Refactors

  • Replace boolean $(shell,...) in configs/Kconfig with $(python,...) that runs Python in-process and returns y/n.
  • Keep COMPILER_TYPE on $(shell,...) since it requires string output.

• Dependencies

  • Remove tools/kconfig submodule; clone Kconfiglib on demand during make config/defconfig (depth=1). Add make distclean to delete the clone.
  • Update CI to stop checking out submodules and ignore tools/kconfig in .gitignore.

^{Written for commit 0a06e45. Summary will update on new commits.}

[cubic-dev-ai]

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