Warn about unused return values that are quite important.

* CI: ArchLinux build should now instrument `-Werror`
 * CI: Increased OpenWrt build verbosity

Signed-off-by: Toni Uhlig <matzeton@googlemail.com>

.github/workflows/build-archlinux.yml

@@ -15,6 +15,8 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
+    env:
+      CMAKE_C_FLAGS: -Werror
     steps:
       - uses: actions/checkout@v3
         with:

.github/workflows/build-openwrt.yml

@@ -57,6 +57,7 @@ jobs:
           FEED_DIR: ${{ github.workspace }}/packages/openwrt
           FEEDNAME: ndpid_openwrt_packages_ci
           PACKAGES: nDPId-testing
+          V: s
 
       - name: Store packages
         uses: actions/upload-artifact@v3