plan9asm: map runtime.memmove to libc

[zhouguangyuan0718]

What changed

• Add an unconditional manual signature for the external runtime.memmove assembly symbol.
• Set its emitted FuncSig.Name to memmove, so LLGo links the call to libc memmove without package- or architecture-specific checks.
• Update the github.com/xgo-dev/plan9asm dependency from v0.3.0 to v0.3.2, which includes the required external-symbol and ARM64 assembly support.
• Add a unit assertion covering the generic manual signature.

Why

github.com/klauspost/compress/s2 uses CALL runtime·memmove(SB) in its amd64 and arm64 assembly. LLGo does not provide the Go runtime symbol runtime.memmove; the corresponding implementation is libc memmove. The previous resolution path could not express this external declaration name without special-casing the resolver.

The newer plan9asm release also carries the assembly support needed by optimized compression dependencies, including the ARM64 instructions used by s2, reedsolomon, and crc64nvme.

Scope

The LLGo change is intentionally limited to extraAsmSigsAndDeclMap: symbol normalization remains generic, and no package path or architecture is used to select the memmove mapping. The dependency update uses the published plan9asm v0.3.2 release, which contains the merged changes from xgo-dev/plan9asm#17.

Validation

• go test ./internal/plan9asm.
• Built the llgo CLI with plan9asm v0.3.2.
• Forced full LLGo builds of github.com/klauspost/compress/s2, github.com/klauspost/reedsolomon, and github.com/minio/crc64nvme using the updated dependency.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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