runtime: don't use cgo_unsafe_args for syscall9 wrapper

It uses less stack space this way.

Similar to CL 386719
Update #71302

Change-Id: I585bde5f681a90a6900cbd326994ab8a122fd148
Reviewed-on: https://go-review.googlesource.com/c/go/+/665695
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

Author: randall77

src/runtime/sys_darwin.go

@@ -70,12 +70,12 @@ func syscall6()
 //
 //go:linkname syscall_syscall9 syscall.syscall9
 //go:nosplit
-//go:cgo_unsafe_args
 func syscall_syscall9(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2, err uintptr) {
+	args := struct{ fn, a1, a2, a3, a4, a5, a6, a7, a8, a9, r1, r2, err uintptr }{fn, a1, a2, a3, a4, a5, a6, a7, a8, a9, r1, r2, err}
 	entersyscall()
-	libcCall(unsafe.Pointer(abi.FuncPCABI0(syscall9)), unsafe.Pointer(&fn))
+	libcCall(unsafe.Pointer(abi.FuncPCABI0(syscall9)), unsafe.Pointer(&args))
 	exitsyscall()
-	return
+	return args.r1, args.r2, args.err
 }
 func syscall9()