SipHash: Avoid new compiler warnings on RHEL7 #360

Job	Run time
build (centos:7, sed -i 's,^mirrorlist=,#,; s,^#baseurl=http://mirror\.centos\.org/centos/$releas...	1m 16s
build (almalinux:8, yum install -y kernel-devel kernel gcc make elfutils-libelf-devel)	1m 32s
build (rockylinux:8, yum install -y kernel-devel kernel gcc make elfutils-libelf-devel)	1m 51s
build (quay.io/centos/centos:stream9, dnf install -y --nobest kernel-devel-matched gcc make)	1m 49s
build (fedora:latest, dnf install -y kernel-devel kernel gcc make elfutils-libelf-devel)	1m 54s
build (alt:sisyphus, apt-get update; apt-get install -y kernel-headers-modules-un-def gcc make li...	50s
build (registry.opensuse.org/opensuse/tumbleweed, zypper -n install -y gcc make kernel-default-de...	59s
build (registry.opensuse.org/opensuse/leap, zypper -n install -y gcc make kernel-default-devel ta...	1m 5s
	11m 16s

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