GoObj: describe fixed alloca roots in statepoint deopts

[zhouguangyuan0718]

Summary

• remove the fixed-stack-home statepoint lowering added for pointer-containing allocas
• preserve deopt location counts and constant values through StackMaps
• define and strictly parse a self-describing 64-bit alloca pointer-map suffix in GoObj
• synthesize Go locals pointer maps directly from the alloca frame location and bitmap
• reject malformed, duplicate, overlapping, non-direct, or out-of-frame records

The memory slot remains authoritative across the call. No statepoint root spill, gc.relocate, or post-call write-back is required for these allocas.

Validation

• rebuilt Debug llc, opt, llvm-ar, LLVM, and llvm-config for X86 and AArch64
• paired GoALLC plugin suite: 45/45 passed
• opt default O2, llc verify-machineinstrs, MIR frame-location checks, GoObj pointer-map checks
• AArch64 wbZero/wbMove disassembly confirms no stale post-call store and no added root spill
• runtime GC and stack-growth fixture passed

Paired producer and end-to-end tests: goallc/go#33.

[github-actions]

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