AOT-safe UndefinedVariableJitHelper guards (#10524)

[PurHur]

Summary

• AOT-safe UndefinedVariableJitHelper guards without broken LLVM bridge (#10360) #10524: Rebased onto current master — incremental AOT-safe guards for undefined-variable warnings.
• Skip duplicate StringTriggerErrorJit::implement when __compiler_trigger_error is already linked in standalone modules (avoids corrupt LLVM module / verify failures on 000-HelloWorld).
• Skip scope-var JIT guards during NestedJitCompileScope (PHP_COMPILER_SELFHOST_AOT=0) so nested ObGzhandler bootstrap does not fatal.
• Document in Context that UndefinedVariableRuntime::ensureStandaloneBodies is intentionally omitted (StringTriggerError already linked).
• Guards route through UndefinedVariableRuntime::emitWarningForName() → UndefinedVariableJitHelper::warningMessage() SSOT + __compiler_trigger_error (no compiled helper bridge ABI mismatch).

php-src reference

• Zend/zend_execute.c — ZEND_CHECK_UNDEFINED_VAR
• PHP: lib/VM/UndefinedVariableJitHelper.php, lib/JIT/Builtin/UndefinedVariableRuntime.php

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
vendor/bin/phpunit test/unit/UndefinedVariableRuntimeShrinkTest.php test/unit/JIT/ScalarDimFetchRuntimeStandaloneTest.php
./script/examples-aot-smoke.sh
'

Results (2026-06-22):

• UndefinedVariableRuntimeShrinkTest — OK (4 tests)
• ScalarDimFetchRuntimeStandaloneTest — OK (1 test)
• examples-aot-smoke — ok (000–006, 008–009 default slice)

Closes #10524

[PurHur]

Merge blocked: origin/master (aa4bfa6) still fails examples-aot-smoke at 000-HelloWorld independently of this patch. This branch (#10498 base + #10524) is green. Recommend landing #10498/#10541 stack first, then rebase this PR.

[PurHur]

Maintainer triage (2026-06-22):

• Merge blocked: GitHub reports `mergeable: CONFLICTING` vs current `master`. Rebase/merge master and re-run `./script/examples-aot-smoke.sh` before merge.
• Bootstrap gates on master (host): `bootstrap-selfhost-link` ✅ · `bootstrap-selfhost-helloworld` ✅ · `bootstrap-inventory.php --check` ❌ (stale `docs/bootstrap-inventory.md`, see Release v1.1.0: regenerate stale docs/bootstrap-inventory.md #10368).
• Local verification plan looks right; please confirm smoke green on rebased branch.

[PurHur]

Maintainer verify 2026-06-22 (branch tip 5d0901b46, pre-rebase):

• ./script/examples-aot-smoke.sh — ok (000-HelloWorld through 009-FastCGIWeb)
• UndefinedVariableRuntimeShrinkTest — 3/3
• ScalarDimFetchRuntimeStandaloneTest — 1/1
• make bootstrap-selfhost-link — ok

Not merged: git merge origin/master hits conflicts; post-merge resolution re-runs smoke red on 000-HelloWorld (LLVM verify: ret i64/i32 and ret %__string__* … i1). Needs rebase onto current master + fix standalone bridge regressions from #10498 follow-ups before merge.

Closes #10524 when green on master.