Minimal GitHub Actions CI setup

.github/workflows/jspecify.yml

@@ -0,0 +1,31 @@
+name: JSpecify JDK CI tests
+
+on:
+  pull_request:
+  push:
+    branches: [ "main" ]
+
+jobs:
+  build_jdk:
+    name: Build the JDK
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    env:
+      JAVA_VERSION: 23
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up JDK 23
+      uses: actions/setup-java@v4
+      with:
+        java-version: 23
+        distribution: 'temurin'
+    - name: Install jtreg
+      run: |
+        wget https://builds.shipilev.net/jtreg/jtreg-7.5%2B1.zip -O /tmp/jtreg.zip
+        unzip /tmp/jtreg.zip -d /tmp/
+    - name: Configure the JDK
+      run: bash ./configure --with-jtreg=/tmp/jtreg --disable-warnings-as-errors
+    - name: Build the JDK
+      run: make jdk
+