submodule: Fix t7400, t7405, t7406 for msysGit

Again, avoid using echo (which issues DOS line endings on msysGit) to not mix
with Unix line-endings issued by git built-ins, even if this is at the cost of
calling an external executable (cat) instead of a shell built-in (echo).

git-submodule.sh

@@ -434,9 +434,11 @@ cmd_add()
 
 	if test -z "$force" && ! git add --dry-run --ignore-missing "$sm_path" > /dev/null 2>&1
 	then
-		eval_gettextln "The following path is ignored by one of your .gitignore files:
-\$sm_path
-Use -f if you really want to add it." >&2
+		cat >&2 <<EOF
+The following path is ignored by one of your .gitignore files:
+$(eval_gettextln $sm_path)
+Use -f if you really want to add it.
+EOF
 		exit 1
 	fi