php-in-php: drop last AOT C TU (phpc_progress.c) by emitting SIGSEGV handler in LLVM

[PurHur]

Goal

Remove the last hand-written C runtime translation unit from the AOT link by emitting the async-signal-safe SIGSEGV handler directly in LLVM IR from PHP lowering (PHP-in-PHP, #1492).

Current behavior

AOT links a bundled C TU that installs a SIGSEGV handler which prints the last progress breadcrumb ("phpc_last_progress") and exits 139.

Change

• Emit phpc_segv_handler in LLVM IR (write(2)+_exit only)
• Install handler during __init__ emission (no __attribute__((constructor)))
• Keep progress breadcrumb globals in LLVM (existing ProgressNoteRuntime)
• Make lib/AOT/Linker.php ship no bundled C runtime sources

Why this is safe

The handler stays async-signal-safe (no malloc/stdio); only write + _exit.

Verification

• ./script/docker-exec.sh ./script/check-aot-build-smoke.sh
• ./script/docker-exec.sh php vendor/bin/phpunit --filter 'AotRuntimeInventoryTest|RuntimeShrinkCloseoutTest|ProgressNoteRuntimeStandaloneTest|ExecJitRuntimeShrinkTest|GettextJitRuntimeShrinkTest|ProgressNoteRuntimeShrinkTest'

Notes

If we need portability beyond Linux, a follow-up could avoid hardcoding SIGSEGV=11 in IR.

[PurHur]

claim: PHP Runtime �1 PHP �1 eliminate last AOT C TU (this run)

[PurHur]

Merged via PR #17149.\n\nVerification:\n- ./script/docker-exec.sh ./script/check-aot-build-smoke.sh\n- ./script/docker-exec.sh php vendor/bin/phpunit --filter 'AotRuntimeInventoryTest|RuntimeShrinkCloseoutTest|ProgressNoteRuntimeStandaloneTest|ExecJitRuntimeShrinkTest|GettextJitRuntimeShrinkTest|ProgressNoteRuntimeShrinkTest'\n- make bootstrap-gen0-refresh-sidecar