RHEL8 package install or build fail

[Jason A. Donenfeld]

This commit fixes it and will be included in the next snapshot:
https://git.zx2c4.com/WireGuard/commit/?id=80f006d3656ce2858675020a23879e916ea8a4fc

[ec2-user at ip-172-31-24-82 ~]$ cat /etc/redhat-release
Red Hat Enterprise Linux release 8.0 (Ootpa)
[ec2-user at ip-172-31-24-82 ~]$ uname -a
Linux ip-172-31-24-82.eu-west-1.compute.internal
4.18.0-80.4.2.el8_0.x86_64 #1 SMP Fri Jun 14 13:20:24 UTC 2019 x86_64
x86_64 x86_64 GNU/Linux
[ec2-user at ip-172-31-24-82 ~]$ sudo ip link add wg0 type wireguard
[ec2-user at ip-172-31-24-82 ~]$ sudo wg
interface: wg0
[ec2-user at ip-172-31-24-82 ~]$ dmesg | grep wireguard
[  693.365784] wireguard: loading out-of-tree module taints kernel.
[  693.382433] wireguard: module verification failed: signature and/or
required key missing - tainting kernel
[  693.390216] wireguard: WireGuard 0.0.20190601-8-g9e71cce-dirty
loaded. See www.wireguard.com for information.
[  693.397561] wireguard: Copyright (C) 2015-2019 Jason A. Donenfeld
<Jason at zx2c4.com>. All Rights Reserved.