runtime: sigctxt.r9 returns the wrong register in signal_netbsd_amd64.go

[Relect]

go/src/runtime/signal_netbsd_amd64.go

Line 29 in da46879

func (c *sigctxt) r9() uint64 { return c.regs().__gregs[_REG_R8] }

[ianlancetaylor]

It's not clearly expressed, but there is a bug here.

[gopherbot]

Change https://go.dev/cl/478135 mentions this issue: runtime: let (*sigctxt).r9 return the correct register value on netbsd