Add a FreeBSD build to CI (#8269)

Playing with this because it's interesting and I learned about this cool
firecracker action.

Related #3370

.github/workflows/ci.yml

@@ -551,6 +551,52 @@ jobs:
           path: ${{ env.UV_WORKSPACE }}/target/debug/uv.exe
           retention-days: 1
 
+  build-binary-freebsd:
+    needs: determine_changes
+    timeout-minutes: 10
+    if: ${{ github.repository == 'astral-sh/uv' && (needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main') }}
+    runs-on:
+      labels: ubuntu-latest
+    name: "build binary | freebsd"
+
+    steps:
+      - uses: actions/checkout@v4
+      - uses: Swatinem/rust-cache@v2
+      - name: "Cross build"
+        run: |
+          # Install cross from `freebsd-firecracker`
+          wget -q -O cross https://github.com/acj/freebsd-firecracker/releases/download/v0.0.10/cross
+          chmod +x cross
+          mv cross /usr/local/bin/cross
+
+          cross build --target x86_64-unknown-freebsd
+
+      - name: Test in Firecracker VM
+        uses: acj/freebsd-firecracker-action@v0.2.0
+        with:
+          verbose: false
+          pre-run: |
+            # The exclude `*` prevents examination of directories so we need to
+            # include each parent directory of the binary
+            include_path="$(mktemp)"
+            cat <<EOF > $include_path
+            target
+            target/x86_64-unknown-freebsd
+            target/x86_64-unknown-freebsd/debug
+            target/x86_64-unknown-freebsd/debug/uv
+            EOF
+
+            rsync -r -e "ssh" \
+              --relative \
+              --copy-links \
+              --include-from "$include_path" \
+              --exclude "*" \
+              . firecracker:
+          run-in-vm: |
+            cp target/x86_64-unknown-freebsd/debug/uv uv
+            chmod +x uv
+            ./uv --version
+
   ecosystem-test:
     timeout-minutes: 10
     needs: build-binary-linux

crates/uv-performance-flate2-backend/Cargo.toml

@@ -6,8 +6,8 @@ publish = false
 [lib]
 doctest = false
 
-[target.'cfg(not(any(target_arch = "s390x", target_arch = "powerpc64")))'.dependencies]
+[target.'cfg(not(any(target_arch = "s390x", target_arch = "powerpc64", target_os = "freebsd")))'.dependencies]
 flate2 = { version = "1.0.28", default-features = false, features = ["zlib-ng"] }
 
-[target.'cfg(any(target_arch = "s390x", target_arch = "powerpc64"))'.dependencies]
+[target.'cfg(any(target_arch = "s390x", target_arch = "powerpc64", target_os = "freebsd"))'.dependencies]
 flate2 = { version = "1.0.28", default-features = false, features = ["rust_backend"] }