Classify explicit toolchain features into shared and platform-specific groups

[nradakovic]

What

Review the current explicit C++ toolchain feature model and classify each feature into one of the following groups:

• shared/common across Linux and QNX
• Linux-specific
• QNX-specific
• consumer-extensible via extra_known_features / extra_enabled_features

This task establishes the architectural boundary needed for the refactoring Epic.

Acceptance Criteria (DoD)

• A documented classification exists for all explicitly modeled toolchain features.
• Each feature is assigned to exactly one primary ownership group.
• The classification identifies which features are safe to share and which must remain platform-specific.
• The result is detailed enough to guide follow-up extraction and refactoring tasks.

How

• Review the current Linux and QNX toolchain templates.
• Enumerate explicitly defined features and note their purpose, enabled state, and action coverage.
• Compare Linux and QNX feature behavior to identify true overlap versus superficial similarity.
• Record the final classification in a maintainer-facing design note or tracking document.