CI: add release workflow

.github/workflows/build-release.yml

@@ -0,0 +1,36 @@
+name: Build Release
+
+on:
+  push:
+    branches: [workflows] # FIXME: replace w/ main before merging
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  build_serial:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+    runs-on: ${{ os }}
+    steps:
+      - uses: actions/checkout@v3
+      - name: Build serial
+        run: cargo build --bin serial --release
+  build_rootshell_and_rayhunter:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          targets: armv7-unknown-linux-gnueabihf
+      - name: Install cross-compilation dependencies
+        run: sudo apt install \
+          build-essential \
+          libc6-armhf-cross \
+          libc6-dev-armhf-cross \
+          gcc-arm-linux-gnueabihf
+      - name: Build rootshell (arm32)
+        run: cargo build --bin rootshell --target armv7-unknown-linux-gnueabihf --release
+      - name: Build rayhunter (arm32)
+        run: cargo build --bin rayhunter-daemon --target armv7-unknown-linux-gnueabihf --release