Automatically build binaries for Popular Linux archs (#253)

* Build Linux binaries on a release

.github/workflows/release-build.yml

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+name: Build Linux Binaries
+
+on:
+  release:
+    types: [published]
+env:
+  MOSQUITTO_VERSION: 2.0.15
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: download mosquitto
+        run: |
+          curl -o mosquitto.tgz https://mosquitto.org/files/source/mosquitto-${{ env.MOSQUITTO_VERSION }}.tar.gz
+          tar -zxf mosquitto.tgz
+          mkdir -p output/linux-amd64 output/linux-arm64 output/linux-armv7 output/linux-armv6
+      - name: Checkout
+        uses: actions/checkout@v3
+        with:
+          path: mosquitto-go-auth
+      - name: run build
+        uses: addnab/docker-run-action@v3
+        with:
+          image: golang:latest
+          options: -e MOSQUITTO_VERSION=${{ env.MOSQUITTO_VERSION }} -v ${{ github.workspace }}:/usr/src -w /usr/src
+          run: |
+            /usr/src/mosquitto-go-auth/.github/workflows/scripts/build.sh
+      - name: zip
+        run: |
+          cd ${{ github.workspace }}/output
+          zip -r linux-amd64.zip linux-amd64
+          zip -r linux-arm64.zip linux-arm64
+          zip -r linux-armv7.zip linux-armv7
+          zip -r linux-armv6.zip linux-armv6
+      - name: Release files
+        uses: softprops/action-gh-release@v1
+        with:
+          files: |
+            output/linux-amd64.zip
+            output/linux-arm64.zip
+            output/linux-armv6.zip
+            output/linux-armv7.zip

.github/workflows/scripts/build.sh

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+#!/bin/bash
+
+apt-get update
+apt-get install -y gcc-arm-linux-gnueabi binutils-arm-linux-gnueabi gcc-aarch64-linux-gnu binutils-aarch64-linux-gnu
+cd /usr/src/mosquitto-$MOSQUITTO_VERSION/include
+cp *.h /usr/include
+cd /usr/src/mosquitto-go-auth
+
+#build amd64 Linux
+make
+cp go-auth.so pw /usr/src/output/linux-amd64
+
+# build arm64 Linux
+make clean
+export CGO_ENABLED=1
+export GOARCH=arm64
+export CC=aarch64-linux-gnu-gcc
+make
+cp go-auth.so pw /usr/src/output/linux-arm64
+
+# build armv7 Linux
+make clean
+export CGO_ENABLED=1
+export GOARCH=arm
+export GOARM=7
+export CC=arm-linux-gnueabi-gcc
+make
+cp go-auth.so pw /usr/src/output/linux-armv7
+
+# build armv7 Linux
+make clean
+export CGO_ENABLED=1
+export GOARCH=arm
+export GOARM=6
+export CC=arm-linux-gnueabi-gcc
+make
+cp go-auth.so pw /usr/src/output/linux-armv6