Rust fixes for v6.9

 - Soundness: make internal functions generated by the 'module!' macro
   inaccessible, do not implement 'Zeroable' for 'Infallible' and
   require 'Send' for the 'Module' trait.

 - Build: avoid errors with "empty" files and workaround 'rustdoc' ICE.

 - Kconfig: depend on '!CFI_CLANG' and avoid selecting 'CONSTRUCTORS'.

 - Code docs: remove non-existing key from 'module!' macro example.

 - Docs: trivial rendering fix in arch table.
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