runtime: add memprofile attribution support

[cpunion]

Summary:

• add a lightweight LLGo runtime memprofile snapshot with synthetic frames for runtime.MemProfile
• preserve heap attribution frames by disabling inline/tail-call elimination for packages using runtime.MemProfile/MemProfileRate
• add stable test/go coverage and un-xfail GOROOT heapsampling.go

Tests:

• go test ./test/go -run TestRuntimeMemProfileAttribution -count=1
• go test ./test/goroot -run TestGoRootRunCases -count=1 -args -goroot /opt/homebrew/Cellar/go@1.24/1.24.11/libexec -dirs . -case '^heapsampling.go$' -directive-mode runlike
• go test ./cl ./ssa
• cd runtime && go test ./internal/lib/runtime ./internal/runtime
• git diff --cached --check

[cpunion]

Verification update for commit 622e1e5:\n\n- Root cause: Linux CI could not reliably recover LLGo Go function names from libunwind for memory profile stack attribution; the profile saw frames like n / __libc_start_main, so TestRuntimeMemProfileAttribution could not find main.profiledAlloc.\n- Fix: for packages that use runtime.MemProfile, the compiler now emits lightweight MemProfileEnter/Exit calls and the runtime uses that Go call stack before falling back to libunwind.\n- Local tests:\n - go test ./test/go -run TestRuntimeMemProfileAttribution -count=1 -v\n - go test ./test/go -count=1\n - go test ./ssa -count=1\n - go test ./cl -count=1\n\nPushed only to cpunion/llgo:codex/goroot-heapsampling-coverage. Monitoring the new CI run now.

[cpunion]

CI update for 622e1e5a0e3eeccd097599b6f4a6abb8639740f9:

• Previously failing test/go memprofile attribution failure is fixed by keeping a lightweight Go call stack for runtime.MemProfile test packages.
• Local verification passed:
  • go test ./test/go -run TestRuntimeMemProfileAttribution -count=1 -v
  • go test ./test/go -count=1
  • go test ./ssa -count=1
  • go test ./cl -count=1
• New CI: the three previously failing jobs now pass:
  • test (ubuntu-latest, 19)
  • test (ubuntu-latest, 19, 1.24.2, 2)
  • test (ubuntu-latest, 19, 1.26.0, 2)

At the time of this update, the remaining visible checks are queued macOS jobs; no new failure is showing on the PR.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 76.66667% with 14 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cl/compile.go	86.53%	4 Missing and 3 partials ⚠️
ssa/memory.go	0.00%	4 Missing ⚠️
ssa/decl.go	0.00%	3 Missing ⚠️

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