add build targets for windows/386 and linux/386

Dockerfile.linux-386

@@ -0,0 +1,9 @@
+ARG GO_VERSION
+FROM golang:$GO_VERSION
+RUN \
+  apt-get update && \
+  apt-get install -y libc6-dev-i386
+
+ENV CGO_ENABLED=1
+ENV GOOS=linux
+ENV GOARCH=386

Dockerfile.windows-386

@@ -0,0 +1,12 @@
+ARG GO_VERSION
+FROM golang:$GO_VERSION
+RUN \
+  apt-get update && \
+  apt-get install -y mingw-w64
+
+ENV CGO_ENABLED=1
+ENV CC=i686-w64-mingw32-gcc
+ENV CXX=i686-w64-mingw32-g++
+ENV GOOS=windows
+ENV GOARCH=386
+

Makefile

@@ -6,12 +6,24 @@ build-windows-amd64:
 push-windows-amd64:
 	docker push ${PROJECT}:${GO_VERSION}-windows-amd64
 
+build-windows-386:
+	docker build --build-arg GO_VERSION=${GO_VERSION} -t ${PROJECT}:${GO_VERSION}-windows-386 -f Dockerfile.windows-386 .
+
+push-windows-386:
+	docker push ${PROJECT}:${GO_VERSION}-windows-386
+
 build-linux-amd64:
 	docker build --build-arg GO_VERSION=${GO_VERSION} -t ${PROJECT}:${GO_VERSION}-linux-amd64 -f Dockerfile.linux-amd64 .
 
 push-linux-amd64:
 	docker push ${PROJECT}:${GO_VERSION}-linux-amd64
 
+build-linux-386:
+	docker build --build-arg GO_VERSION=${GO_VERSION} -t ${PROJECT}:${GO_VERSION}-linux-386 -f Dockerfile.linux-386 .
+
+push-linux-386:
+	docker push ${PROJECT}:${GO_VERSION}-linux-386
+
 build-linux-arm-7:
 	docker build --build-arg GO_VERSION=${GO_VERSION} -t ${PROJECT}:${GO_VERSION}-linux-arm-7 -f Dockerfile.linux-arm-7 .
 
@@ -24,5 +36,5 @@ build-linux-arm64:
 push-linux-arm64:
 	docker push ${PROJECT}:${GO_VERSION}-linux-arm64
 
-build: build-linux-amd64 build-linux-arm-7 build-linux-arm64 build-windows-amd64
-push:  push-linux-amd64  push-linux-arm-7  push-linux-arm64  push-windows-amd64
+build: build-linux-amd64 build-linux-arm-7 build-linux-arm64 build-linux-386 build-windows-amd64 build-windows-386
+push:  push-linux-amd64  push-linux-arm-7  push-linux-arm64  push-linux-386  push-windows-amd64  push-windows-386