CI: add FreeBSD build

.github/workflows/non_native.yml

@@ -0,0 +1,42 @@
+name: Non-native builds
+
+on:
+  push:
+      paths-ignore:
+          - 'docs/**'
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+
+jobs:
+  freebsd:
+    name: 'FreeBSD (${{ matrix.compiler }}, ${{ matrix.arch }})'
+    runs-on: ubuntu-latest
+    timeout-minutes: 60
+    strategy:
+      matrix:
+        include:
+          - { arch: 'x86_64', compiler: 'clang' }
+          - { arch: 'arm64', compiler: 'clang' }
+      fail-fast: false
+    steps:
+      - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4
+
+      - uses: cross-platform-actions/action@cdc9ee69ef84a5f2e59c9058335d9c57bcb4ac86 # v0.25.0
+        with:
+          operating_system: 'freebsd'
+          version: '14.1'
+          architecture: ${{ matrix.arch }}
+          run: |
+            # https://ports.freebsd.org/
+            sudo pkg install -y cmake ninja pkgconf tiff curl sqlite3
+            cmake -B bld -G Ninja \
+              '-DCMAKE_C_COMPILER=${{ matrix.compiler }}' \
+              -DCMAKE_UNITY_BUILD=ON \
+            cmake --build bld
+            ctest --build bld