Stdlib: JIT set_error_handler / restore_error_handler (North Star 2)

[PurHur]

Summary

• Implement LLVM/JIT lowering for set_error_handler() and restore_error_handler() with compile-time string user-function callbacks (wave 3 Stdlib: set_error_handler() — VM + LLVM JIT/AOT #1379).
• Add lib/AOT/runtime/phpc_error_handler.c and wire trigger_error() JIT path through __compiler_trigger_error → user handler dispatch.
• Grow M2 spine smoke bundle by 2 units (JitErrorHandler, ErrorHandlerOutput) — 595/603 toward full inventory.
• VM compliance unchanged; JIT PHPTs + ErrorHandlerJITTest added for when MCJIT runtime symbols resolve.

Closes #1379

North Star alignment

Supports #1492 / #1056 (self-host): error-handler builtins are no longer VM-only deferred in SelfHostBuiltinPolicy; spine includes new JIT leaf modules.

Test plan

• vendor/bin/phpunit --filter ErrorHandler (VM PHPTs)
• php bin/compile.php -l test/selfhost/compiler_lib_spine_smoke/main.php
• ./script/ci-fast.sh --filter ErrorHandler in Docker (php-compiler:22.04-dev)
• Full ./script/ci-local.sh (LLVM) on merge host

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