CI: add Github workflow

Use the 'zulu' JDK distribution which
provides both LTS and non-LTS versions
of the JDK.

.github/workflows/build.yml

@@ -0,0 +1,22 @@
+on:
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        java: [ '11', '17' ]
+    name: Java ${{ matrix.Java }} sample
+    steps:
+      - uses: actions/checkout@v3
+      - name: Setup java
+        uses: actions/setup-java@v3
+        with:
+          distribution: 'zulu'
+          java-version: ${{ matrix.java }}
+      - name: Build MSPSim
+      - run: ant compile
+      - name: Test MSPSim
+      - run: ant test