M5 spine link: refuse Zend inventory rebuild when NO_ZEND_FALLBACK set (#8716)

[PurHur]

Summary

• bootstrap_ensure_inventory_argv_driver now fails closed when BOOTSTRAP_NO_ZEND_FALLBACK=1 (previously only BOOTSTRAP_M5_NO_ZEND=1), blocking the Zend helloworld-compile-bin rebuild path (Self-host M5: PHP_COMPILER_LIB_SPINE_BUNDLE compile path — no Zend gen-0 fallback in CI #8716).
• bootstrap-selfhost-lib-spine-smoke-link.sh falls back to native driver resolver when prelinked inventory smoke fails instead of hard-exiting before the compile step.
• Fix ObGzhandlerJitRuntime::emitResolveEncoding() PHI dominance (resolveDoneBb incoming block) that caused LLVM verify failure during inventory argv driver rebuild.
• Document BOOTSTRAP_NO_ZEND_FALLBACK=1 for lib spine smoke; add bootstrap script unit assertions.

Closes #8716

Test plan

# Unit guards (pass)
./vendor/bin/phpunit test/unit/BootstrapSelfhostLinkTest.php --filter testLinkScriptUsesCompiledDriverResolver
./vendor/bin/phpunit test/unit/BootstrapLibSpineVmSmokeTest.php --filter testLibSpineLinkScriptSeedsSidecarsAndRefusesZendFallback

# Bootstrap gates
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && make bootstrap-selfhost-link'
# OK bootstrap-selfhost-link: OK /compiler/build/selfhost

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && BOOTSTRAP_NO_ZEND_FALLBACK=1 make bootstrap-selfhost-lib-spine-smoke'
# Still blocked: stale prelinked .m3_compiler_lib_sidecar.sha vs spine entry (#8820) + native parseAndCompile null at c:main_before_php; sidecar fallback correctly refuses stale stamp (#2201). Master fails the same gate even with Zend fallback enabled.

Merge blocker (follow-up)

Refresh prelinked/bootstrap-gen0/ sidecar stamp+blob after spine entry #8820, or fix native spine compile null — then re-run BOOTSTRAP_NO_ZEND_FALLBACK=1 make bootstrap-selfhost-lib-spine-smoke and make north-star5-verify-fast.

Made with Cursor

[PurHur]

Maintainer: merged after local verification — both unit tests green, bootstrap-selfhost-link OK on branch.