builds: use same docker image for Arm and Windows builds

Both can be done using the same Rust "cross" tool.

build.sh

@@ -67,10 +67,14 @@ build_linux() {
            ${TAG} make dist rpm deb
 }
 
-build_linux_armv7() {
-    DOCKERFILE="./docker/builder/Dockerfile.armv7"
-    TAG=${BUILDER_TAG:-"evebox/builder:armv7"}
-    TARGET="armv7-unknown-linux-musleabihf"
+build_cross() {
+    target="$1"
+    if [ "${target}" = "" ]; then
+        echo "error: target must be set for build_cross"
+        exit 1
+    fi
+    DOCKERFILE="./docker/builder/Dockerfile.cross"
+    TAG=${BUILDER_TAG:-"evebox/builder:cross"}
     docker build --rm \
            --cache-from ${TAG} \
 	   -t ${TAG} \
@@ -83,53 +87,21 @@ build_linux_armv7() {
          -e REAL_UID="$(id -u)" \
          -e REAL_GID="$(id -g)" \
          -e BUILD_REV="${BUILD_REV}" \
-         -e TARGET="${TARGET}" \
+         -e TARGET="${target}" \
          -e CARGO="cross" \
          ${TAG} make dist
 }
 
 build_linux_armv8() {
-    DOCKERFILE="./docker/builder/Dockerfile.armv7"
-    TAG=${BUILDER_TAG:-"evebox/builder:armv8"}
-    TARGET="aarch64-unknown-linux-musl"
-    docker build --rm \
-           --cache-from ${TAG} \
-	   -t ${TAG} \
-	   -f ${DOCKERFILE} .
-    docker run ${IT} --rm \
-         -v "$(pwd)/target/docker/${TARGET}:/src/target:z" \
-         -v "$(pwd)/dist:/src/dist:z" \
-         -v /var/run/docker.sock:/var/run/docker.sock \
-         -w /src \
-         -e REAL_UID="$(id -u)" \
-         -e REAL_GID="$(id -g)" \
-         -e BUILD_REV="${BUILD_REV}" \
-         -e TARGET="${TARGET}" \
-         -e CARGO="cross" \
-         ${TAG} make dist
+    build_cross aarch64-unknown-linux-musl
 }
 
+build_linux_armv7() {
+    build_cross armv7-unknown-linux-musleabihf
+}
 
 build_windows() {
-    TAG=${BUILDER_TAG:-"evebox/builder:windows"}
-    DOCKERFILE="./docker/builder/Dockerfile.windows"
-    TARGET="x86_64-pc-windows-gnu"
-    docker build ${CACHE_FROM} --rm \
-           --build-arg REAL_UID="$(id -u)" \
-           --build-arg REAL_GID="$(id -g)" \
-           --cache-from ${TAG} \
-	   -t ${TAG} \
-	   -f ${DOCKERFILE} .
-    docker run ${IT} --rm \
-           -v "$(pwd)/target/docker/${TARGET}:/src/target:z" \
-           -v "$(pwd)/dist:/src/dist:z" \
-           -w /src \
-           -e REAL_UID="$(id -u)" \
-           -e REAL_GID="$(id -g)" \
-           -e CC=x86_64-w64-mingw32-gcc \
-           -e TARGET=x86_64-pc-windows-gnu \
-           -e BUILD_REV="${BUILD_REV}" \
-           ${TAG} make dist
+    build_cross x86_64-pc-windows-gnu
 }
 
 build_macos() {