Report which submodule check failed in build.sh instead of exiting silently

packaging/build.sh

@@ -17,8 +17,10 @@ git config --global --add safe.directory "$root"
 for source in libg15 libg15render g15daemon g15macro g15stats; do
     git config --global --add safe.directory "$root/$source"
     pin=$(git -C "$root" ls-files --stage -- "$source" | awk '$1 == 160000 {print $2}')
-    [[ -n $pin && $(git -C "$root/$source" rev-parse HEAD) == "$pin" ]]
-    [[ -z $(git -C "$root/$source" status --porcelain --untracked-files=all) ]]
+    [[ -n $pin && $(git -C "$root/$source" rev-parse HEAD) == "$pin" ]] \
+        || { echo "$source: HEAD does not match the committed gitlink pin" >&2; exit 1; }
+    [[ -z $(git -C "$root/$source" status --porcelain --untracked-files=all) ]] \
+        || { echo "$source: submodule has uncommitted or untracked changes; commit or stash them first" >&2; exit 1; }
 done
 git -C "$root" submodule status --recursive -- libg15 libg15render g15daemon g15macro g15stats > "$out/SUBMODULES"
 if grep -q '^[+U-]' "$out/SUBMODULES"; then echo 'Submodule pin mismatch or missing module' >&2; exit 1; fi