unix: disable sysctl on iOS

Running the regenerating scripts also brought in ClockGettime.

Updates golang/go#34133

Change-Id: I0eb9ed6dbbc2bdd7e3d2a7f5d88492e9dfed0ada
Reviewed-on: https://go-review.googlesource.com/c/sys/+/194097
Run-TryBot: Elias Naur <mail@eliasnaur.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/syscall_darwin_arm64.go

@@ -14,6 +14,10 @@ func ptrace(request int, pid int, addr uintptr, data uintptr) error {
 	return ENOTSUP
 }
 
+func sysctl(mib []_C_int, old *byte, oldlen *uintptr, new *byte, newlen uintptr) error {
+	return ENOTSUP
+}
+
 func setTimespec(sec, nsec int64) Timespec {
 	return Timespec{Sec: sec, Nsec: nsec}
 }