build: Quiet errors from realpath

If the output directory doesn't exist yet realpath will print a warning,
suppress it.

Author: mpe

build/scripts/lib.sh

@@ -89,7 +89,7 @@ function get_output_dir()
         d="$d@$version"
     fi
 
-    d=$(realpath $d)
+    d=$(realpath -q $d)
     echo "$d"
 
     return 0