plan9: replace Exit assembly stub with os.Exit

[Jah-yee]

Fix: golang/go#78506 — plan9.Exit build failure

Problem: Cross-compiling to GOOS=plan9 GOARCH=amd64 fails with:

# golang.org/x/sys/plan9.exit: relocation target syscall.exit not defined

The Exit function uses assembly (asm_plan9_amd64.s) that references syscall.exit, which does not exist on Plan 9.

Solution: Replace the assembly stub with a direct Go call to os.Exit, which properly terminates the process. Also remove the now-orphaned asm_plan9_amd64.s file.

Changes:

• plan9/syscall_plan9.go: Replace assembly-based exit stub with os.Exit(code)
• plan9/asm_plan9_amd64.s: Removed (only existed for the Exit function)

Note: The 386 and arm assembly files still have the same exit stub issue. This PR only fixes amd64. Follow-up PRs can address the other architectures if needed.

Fixes golang/go#78506

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Message from Cherry Mui:

Patch Set 1: Hold+1

(1 comment)

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Message from Ian Lance Taylor:

Patch Set 1:

(1 comment)

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