hack: explicitly control enabling the journald logging driver

Without this, the dependency on systemd is said to be "automagic", which
can lead to breakage, for example, if a binary package of docker is
built on a system that has systemd installed then installed on a system
that does not have systemd installed.

for example: https://bugs.gentoo.org/914076

closes #47770

hack/make.sh

@@ -83,7 +83,7 @@ if [ ! "$GOPATH" ]; then
  exit 1
 fi
 
-if ${PKG_CONFIG} 'libsystemd' 2> /dev/null; then
+if [[ ${SYSTEMD:-1} == 1 ]] && ${PKG_CONFIG} 'libsystemd' 2> /dev/null; then
  DOCKER_BUILDTAGS+=" journald"
 fi