Bootstrap TODO

TCC parity and cc.scm cleanup

• Restore strict tcc-cc parity: every C construct accepted by cc.scm must also be accepted by the bundled TCC.
• Remove raw _Static_assert, _Noreturn, _Alignas, and C11 _Alignof support from cc.scm; have the Kit bootstrap configuration erase or map those spellings before either compiler sees them.
• Replace Kit's __builtin_offsetof dependency with a portable offsetof macro, then remove the builtin parser support.
• Rewrite Kit's three nested-designator initializers and four file-scope slice compound initializers, then remove their special handling and the now-unused file-scope unevaluated-expression walker from cc.scm.
• Retain only the ordered, non-overlapping array-designator behavior Kit needs; keep the aggregate ABI, arithmetic, sizeof, namespacing, static-local, function-buffer, and variadic correctness changes.
• Rewrite or remove 346-c11-decl-align and run the complete cc and tcc-cc suites after the language subset is reduced.

Kit bootstrap profiles

• Add a test that uses tcc to compile the kit0 TUs so that we reject surviving unsupported C11/builtin tokens in Kit's generated translation units.
• Add a test that uses kit0 to compile TCC (so that each can compile the other)
• Add Kit x64 and rv64 bootstrap profiles matching boot2's amd64 and riscv64 mappings, then run compile, link, smoke, and fixed-point checks for all three 64-bit targets.