[Go] Model runtime stack semantics and entry maps

[zhouguangyuan0718]

Summary

• use go-nosplit as the sole opt-out from the native Go stack check; split functions call runtime.morestack*<ABI0> with an ordinary target call
• emit one function-level EntryArgsStackMapID record for every GoObj Go function, independent of split/nosplit behavior
• serialize the entry map as map 0 and use the Machine-CFG-derived PCSP stream to restore map 0 on entry-stack-depth paths, without identifying runtime.morestack* in GoObj emission
• serialize ordinary statepoints as additional live maps and let same-PC statepoints override a CFG map-0 transition
• retain complete ABI register homes for morestack retries while omitting unused, potentially poison incoming pointer values from the entry GC bitmap
• model go-systemstack with g.stackguard1 and runtime.morestackc

Stack position

This is 2/3 in the runtime LLVM support stack.

Depends on #77.
Next/final layer: #76, X86 ABI0/ABIInternal boundary repair.

#75 has been folded into this PR so the stack semantics and the entry-map contract can be reviewed as one coherent change.

Testing

• fresh Release build of llc for X86 and AArch64
• 12 GoObjStackMapUtilsTest unit tests
• 38 Generic/X86/AArch64 GoObj codegen tests
• dedicated object test covering map 0 -> ordinary map 1 -> CFG-derived map 0 on both targets

[github-actions]

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