Work around a gcc5 bug

Work around a gcc5 bug

The old code produced crashes with gcc5 caused by calling the copy
constructor (see https://bugzilla.redhat.com/show_bug.cgi?id=1260976).
This has been filed as gcc bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67557
It is currently being marked as invalid (they claim the code is not valid and
produces undefined behaviour), but I don't think that this is correct.
Fortunately i does not matter for us whether the old code was valid or not,
since the new version is easier to understand and works with all compilers.