Fix CallArgv lazy init blocking spine/AOT compile (#197)

[PurHur]

Summary

• Native::call() always emits CallArgv::emitStore() for func_get_args/func_num_args support (Language: Variadic functions (...$args) and func_get_args() #197), but CallArgv::implement() was only reached via Type::ensureExternals().
• Spine/AOT compile aborted at c:main_before_php with LogicException: CallArgv global not initialized.
• Fix: lazy-init the LLVM global in emitStore() / load() (idempotent implement()), matching other JIT helper patterns.

Verification

./script/docker-exec.sh -- bash -lc './vendor/bin/phpunit --filter func_get_args_count_jit'
# OK (2 tests, 2 assertions)

./script/docker-exec.sh -- bash -lc 'make bootstrap-selfhost-link'
# bootstrap-selfhost-link: OK /compiler/build/selfhost

./script/docker-exec.sh -- bash -lc 'make bootstrap-selfhost-vm-driver-execute-probe'
# bootstrap-selfhost-vm-driver-execute-probe: OK /compiler/build/selfhost-lib-spine-smoke

Bootstrap fallback context: make bootstrap-loop-probe was red on lib spine smoke due to this compile abort; full loop-probe still blocked on separate native parseAndCompile null + stale sidecar (#8559).

Refs #1492, #197

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