Add Linux LSM UAPI bindings

[a-shannon]

Summary

• Include <linux/lsm.h> for Linux 6.8 and later.
• Generate lsm_ctx and the 23 LSM ID, attribute, and flag constants
  for all 20 supported architectures.
• Keep the change within the existing general module.

The definitions match the Linux v6.17 UAPI.

Validation

• An unchanged clang 22 baseline regenerates byte-clean.
• Candidate regeneration is idempotent and strips exactly to the upstream base.
• Feature/MSRV checks, the layout oracle, representative cross-target checks,
  and the applicable upstream target matrix pass.

Scope

This exposes raw UAPI definitions only. It does not add syscall wrappers,
detect active LSMs, parse returned records, establish buffer bounds, or claim
runtime kernel support.

Coordination

This is functionally separate from #186, #187, #190, and #182, but those pull
requests overlap generated outputs. I will rebase and regenerate if any of them
land first.

[a-shannon]

Hi @sunfishcode — this PR is now ready for review. GitHub Actions currently show no checks, presumably because this is a first-time fork contribution. When convenient, could you please approve the workflow run and review whether these Linux LSM UAPI bindings fit the existing general module? I am happy to adjust the patch if needed. Thanks!