ci: build samples/cpp/hello_world as part of the multiplatform test

Build the C++ version of the Hello, World sample as part of the
multiplatform (build) test in CI.

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>

.github/workflows/hello_world_multiplatform.yaml

@@ -29,6 +29,12 @@ jobs:
         os: [ubuntu-22.04, ubuntu-24.04, macos-13, macos-14, windows-2022]
     runs-on: ${{ matrix.os }}
     steps:
+      - name: Install packages
+        if: startsWith(runner.os, 'Linux')
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y g++-multilib
+
       - name: Checkout
         uses: actions/checkout@v4
         with:
@@ -68,7 +74,7 @@ jobs:
           elif [ "${{ runner.os }}" = "Windows" ]; then
             EXTRA_TWISTER_FLAGS="-P native_sim --short-build-path -O/tmp/twister-out"
           fi
-          ./scripts/twister --force-color --inline-logs -T samples/hello_world -v $EXTRA_TWISTER_FLAGS
+          ./scripts/twister --force-color --inline-logs -T samples/hello_world -T samples/cpp/hello_world -v $EXTRA_TWISTER_FLAGS
 
       - name: Upload artifacts
         if: failure()
@@ -77,3 +83,4 @@ jobs:
           if-no-files-found: ignore
           path:
             zephyr/twister-out/*/samples/hello_world/sample.basic.helloworld/build.log
+            zephyr/twister-out/*/samples/cpp/hello_world/sample.cpp.helloworld/build.log