Fix stack object finalizer liveness

[cpunion]

Summary

• implement runtime.SetFinalizer on top of BDWGC finalizers and run queued Go finalizers during runtime.GC
• add scoped conservative stack/register cleanup for command-line LLGo programs to address stack object/finalizer liveness cases
• add stable test/go coverage for finalizer behavior and stack-object liveness, and un-xfail the verified darwin/arm64 goroot cases

Tests

• go install ./...
• go test ./test/go -run 'TestRuntimeSetFinalizer' -count=1 -v
• LLGO_ROOT=/Users/lijie/source/goplus/llgo-wt-goroot-stackobj llgo test -run 'TestRuntimeSetFinalizer' -timeout=20m -count=1 ./test/go
• go test -v ./test/goroot -run '^TestGoRootRunCases$' -goroot $(go env GOROOT) -case '^(deferfin|tinyfin|stackobj|stackobj3)\.go$' -xfail /tmp/llgo-empty-xfail.yaml -count=1 -build-timeout 5m -run-timeout 20s -progress 20s
• go test ./cl ./ssa ./test/goroot -run 'Test(ParseDirective|XFail)' -count=1
• go test ./cl ./ssa -count=1
• git diff --check

Notes

• The conservative liveness cleanup is intentionally limited to command-line-arguments; the test/go subprocess probe keeps coverage stable even without the full goroot workflow.
• Linux goroot xfails for these cases are left in place because this pass was verified locally on darwin/arm64 only.

[cpunion]

Updated with Linux pthread feature macro fix in runtime/internal/lib/runtime/_wrap/runtime.c so pthread_getattr_np is declared on glibc-based CI.

Local verification:

• go test ./test/go -run 'TestRuntimeSetFinalizer' -count=1 -v
• go run -tags=dev ./cmd/llgo test -run 'TestRuntimeSetFinalizer' -timeout=20m -count=1 ./test/go
• go test ./cl ./ssa -count=1
• git diff --check

[cpunion]

Updated again after LLGo shard 2 exposed a link failure from compiler-injected stack liveness helpers.

Fixes in 36044708d:

• emit calls to the C runtime wrapper symbols directly instead of skipped Go helper wrappers
• only enable conservative stack liveness clearing for command-line-arguments packages that actually call runtime.SetFinalizer, avoiding unrelated test/go programs pulling in the helper symbol

Local verification:

• LLGO_BUILD_CACHE=off go test ./test/go -run 'TestRuntimeSetFinalizerStackObjectLiveness|TestStringConversionFromWideIntegers' -count=1 -v
• go test ./cl ./ssa -count=1
• git diff --check

Note: LLGO_BUILD_CACHE=off go run -tags=dev ./cmd/llgo test ... reached program execution locally but hit a macOS temp-dir cleanup error (operation not permitted) after the target code path; the plain Go test wrapper passed the same LLGo programs.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 47.98489% with 1239 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
benchmark/runtime_funcinfo/main.go	0.00%	672 Missing ⚠️
internal/pclnpost/binary.go	12.91%	181 Missing and 1 partial ⚠️
internal/pclnpost/write.go	0.00%	150 Missing ⚠️
internal/pclnpost/fixups.go	0.00%	125 Missing ⚠️
cl/compile.go	91.25%	28 Missing and 23 partials ⚠️
internal/pclnpost/pclnpost.go	0.00%	22 Missing ⚠️
internal/pclntab/pclntab.go	61.40%	11 Missing and 11 partials ⚠️
cl/instr.go	96.98%	10 Missing and 5 partials ⚠️

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[cpunion]

Rebased onto #2016 (codex/pclntab-linkphase-p1, which includes #2012) per the review-order plan: #2012 → #2016 → this line of semantics fixes. Conflicts resolved were additive (context fields, the noinline condition set, and runtime.Panic now calls SavePanicCallerFrames() before the panic-node bookkeeping). Note the PR base is still main, so the diff shows #2012/#2016 commits until those merge.