Add a custom github action to build and test zstd-jni under qemu

in order to cover platforms not available in github actions.

.github/actions/qemu-cross/action.yml

@@ -0,0 +1,14 @@
+name: 'QEMU Cross'
+description: 'Compile and test under QEMU'
+inputs:
+  platform:
+    description: 'qemu guest os'
+    required: true
+runs:
+  using: 'composite'
+  steps:
+    - run: ${{ github.action_path }}/docker.sh
+      shell: bash
+      env:
+        PLATFORM_NAME: ${{ inputs.platform }}
+        HOST_WORKSPACE_DIR: ${{ github.workspace }}

.github/actions/qemu-cross/build.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+set -e
+
+apt-get update
+apt-get install -y gcc
+./sbt -v test package

.github/actions/qemu-cross/docker.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+set -e
+
+docker run --rm \
+    --platform ${PLATFORM_NAME} \
+    --name qemu-cross-${PLATFORM_NAME} \
+    --mount type=bind,source=${HOST_WORKSPACE_DIR},target=/github_workspace \
+    --workdir /github_workspace \
+    ${PLATFORM_NAME}/eclipse-temurin:11-jdk-focal ./.github/actions/qemu-cross/build.sh

.github/workflows/ci-qemu-cross.yml

@@ -0,0 +1,18 @@
+name: "CI qemu cross"
+on: [push, pull_request]
+jobs:
+    qemu-cross:
+        strategy:
+            matrix:
+                include: [
+                    { platform: s390x }
+                ]
+        runs-on: ubuntu-latest
+        steps:
+        - uses: actions/checkout@v2
+        - uses: docker/setup-qemu-action@v1
+
+        - name: qemu ${{ matrix.platform }} build and test
+          uses: ./.github/actions/qemu-cross
+          with:
+            platform: ${{ matrix.platform }}