Add CI job for mullvad-ios

Author: dlon

.github/workflows/daemon.yml

@@ -175,3 +175,21 @@ jobs:
           # doesn't run out of space on the D drive.
           CARGO_TARGET_DIR: "C:/cargo-target"
         run: ./ci/check-rust.sh
+
+  build-ios-ffi:
+    runs-on: macos-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1.0.6
+        with:
+          toolchain: stable
+          target: aarch64-apple-ios
+          default: true
+
+      - name: Build and test crates
+        run: |
+          source env.sh
+          cargo build --locked --verbose --lib -p mullvad-ios