enable cross build

Dockerfile.dapper

@@ -24,6 +24,7 @@ ENV DAPPER_SOURCE /go/src/github.com/rancher/rke/
 ENV DAPPER_RUN_ARGS --privileged -v /var/lib/docker
 ENV DAPPER_OUTPUT ./bin ./dist
 ENV DAPPER_DOCKER_SOCKET true
+ENV DAPPER_ENV TAG REPO GOOS CROSS
 ENV TRASH_CACHE ${DAPPER_SOURCE}/.trash-cache
 ENV HOME ${DAPPER_SOURCE}
 WORKDIR ${DAPPER_SOURCE}

scripts/build

@@ -5,6 +5,28 @@ source $(dirname $0)/version
 
 cd $(dirname $0)/..
 
+OS_PLATFORM_ARG=(linux darwin)
+OS_ARCH_ARG[linux]="amd64 arm"
+OS_ARCH_ARG[windows]="386 amd64"
+OS_ARCH_ARG[darwin]="amd64"
+
 mkdir -p bin
 [ "$(uname)" != "Darwin" ] && LINKFLAGS="-linkmode external -extldflags -static -s"
 CGO_ENABLED=0 go build -ldflags "-X main.VERSION=$VERSION $LINKFLAGS" -o bin/rke
+
+if [ -n "$CROSS" ]; then
+    rm -rf build/bin
+    mkdir -p build/bin
+    for OS in ${OS_PLATFORM_ARG[@]}; do
+        for ARCH in ${OS_ARCH_ARG[${OS}]}; do
+            OUTPUT_BIN="build/bin/rke_$OS-$ARCH"
+            if test "$OS" = "windows"; then
+                OUTPUT_BIN="${OUTPUT_BIN}.exe"
+            fi
+            echo "Building binary for $OS/$ARCH..."
+            GOARCH=$ARCH GOOS=$OS CGO_ENABLED=0 go build \
+                  -ldflags="-w -X main.VERSION=$VERSION" \
+                  -o ${OUTPUT_BIN} ./
+        done
+    done
+fi