ci: Test *BSD build

Tests on OpenBSD, FreeBSD and NetBSD. Both x86-64 and arm64 are used.

.github/workflows/build_bsd.yml

@@ -0,0 +1,50 @@
+name: Build on *BSD
+
+on: [push]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        os:
+          - name: openbsd
+            architecture: x86-64
+            version: '7.6'
+
+          - name: openbsd
+            architecture: arm64
+            version: '7.6'
+
+          - name: freebsd
+            architecture: x86-64
+            version: '14.1'
+
+          - name: freebsd
+            architecture: arm64
+            version: '14.1'
+
+          - name: netbsd
+            architecture: x86-64
+            version: '10.0'
+                                                                                                                                                                                                              -          - name: netbsd
+            architecture: arm64
+            version: '10.0'
+
+      steps:
+        - uses: actions/checkout@v4
+
+        - name: Build on ${{ matrix.os.name }} / ${{ matrix.os.architecture }}
+          uses: cross-platform-actions/action@v0.25.0
+          with:
+            environment_variables: MY_ENV1 MY_ENV2
+            operating_system: ${{ matrix.os.name }}
+            architecture: ${{ matrix.os.architecture }}
+            version: ${{ matrix.os.version }}
+            shell: bash
+            memory: 5G
+            cpu_count: 4
+            run: |
+              autoreconf -vfi
+              ./configure
+              make