Migrate the two #foreign-bearing diagnostic tests whose assertions survive the
cutover, with INTENTIONAL snapshot regens (reviewed):
- 1172 (foreign-symbol-conflict): decl '#foreign libc "getenv"' → 'extern libc
"getenv"'. Still tests the dup-C-symbol conflict; the 'foreign symbol already
bound' message is the keyword-neutral INTERNAL wording (renamed to 'extern symbol'
in Phase 9.1), so it persists — only the echoed source line + caret moved.
- 1228 (non-transitive C-import visibility): its identity was the #foreign≡extern
equivalence lock, now historical (structural via the A→B gate + unified AST). The
identifier 'c_foreign_abs' itself contained 'foreign' (would fail the Phase 9.4
gate), so converted c.sx/b.sx/main to two foreign-free extern symbols
(c_abs_one/c_abs_two); still pins per-symbol non-transitive visibility.
Reverted the orthogonal 0→1-byte empty-stdout normalization on 1228/1231 (known
writeGolden idempotency quirk, not a behavior change). Suite green (647/444).
Cross-module example (main → b → c) referencing c's lib-less C imports
transitively. The non-transitive C-import gate (lower/decl.zig
c_import_bare) must police the legacy `#foreign` form and the new
`extern` keyword IDENTICALLY — same 'C function not visible' diagnostic,
not the generic top-level-name wording. Today the extern twin escapes the
c_import_bare gate (body is an empty block, not foreign_expr) and is only
caught by the general isNameVisible gate, yielding the generic message.
Expected snapshot pins the DESIRED equivalent wording; the next commit
aligns the gate to green it. Prerequisite for migrating the fn-decl
`#foreign` path onto `extern`.
443/444 corpus (1228 xfail), 444 unit.
