Add s390x to cross platforms target

Update build script and buid environment for supporting s390x
Signed-off-by: Frédéric Dalleau <frederic.dalleau@docker.com>

Dockerfile

@@ -98,13 +98,15 @@ RUN dpkg --add-architecture arm64
 RUN dpkg --add-architecture armel
 RUN dpkg --add-architecture armhf
 RUN dpkg --add-architecture ppc64el
+RUN dpkg --add-architecture s390x
 RUN --mount=type=cache,sharing=locked,id=moby-cross-true-aptlib,target=/var/lib/apt \
     --mount=type=cache,sharing=locked,id=moby-cross-true-aptcache,target=/var/cache/apt \
         apt-get update && apt-get install -y --no-install-recommends \
             crossbuild-essential-arm64 \
             crossbuild-essential-armel \
             crossbuild-essential-armhf \
-            crossbuild-essential-ppc64el
+            crossbuild-essential-ppc64el \
+            crossbuild-essential-s390x
 
 FROM cross-${CROSS} as dev-base
 
@@ -135,7 +137,8 @@ RUN --mount=type=cache,sharing=locked,id=moby-cross-true-aptlib,target=/var/lib/
             libapparmor-dev:arm64 \
             libapparmor-dev:armel \
             libapparmor-dev:armhf \
-            libapparmor-dev:ppc64el
+            libapparmor-dev:ppc64el \
+            libapparmor-dev:s390x
 
 FROM runtime-dev-cross-${CROSS} AS runtime-dev
 

hack/make/.binary

@@ -69,7 +69,10 @@ hash_files() {
 				export CC="${CC:-powerpc64le-linux-gnu-gcc}"
 				export CGO_ENABLED=1
 				;;
-
+			linux/s390x)
+				export CC="${CC:-s390x-linux-gnu-gcc}"
+				export CGO_ENABLED=1
+				;;
 		esac
 	fi
 

hack/make/cross

@@ -12,7 +12,7 @@ if [ -x "${DEST}/../binary-daemon/dockerd-${VERSION}" ]; then
 	echo "Created symlinks:" "${DEST}/linux/${arch}/"*
 fi
 
-DOCKER_CROSSPLATFORMS=${DOCKER_CROSSPLATFORMS:-"linux/amd64 windows/amd64 linux/ppc64le"}
+DOCKER_CROSSPLATFORMS=${DOCKER_CROSSPLATFORMS:-"linux/amd64 windows/amd64 linux/ppc64le linux/s390x"}
 
 for platform in ${DOCKER_CROSSPLATFORMS}; do
 	(