Add a GitHub Actions build workflow (#19)

.github/workflows/build.yml

@@ -0,0 +1,23 @@
+
+name: Build
+on: [push, pull_request]
+
+jobs:
+  linux:
+    name: Linux
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+        
+      - name: Autogen
+        run: ./autogen.sh
+        
+      - name: Configure
+        run: ./configure --enable-jit --enable-pcre2-8 --enable-pcre2-16 --enable-pcre2-32
+        
+      - name: Build
+        run: make
+        
+      - name: Test
+        run: make check