This fixes build breakages when using standard-conforming build, e.g.
-std=c++11.
Reported-by: Stéphane Ancelot <sancelot@numalliance.com>
Reported-by: Cris Almaraz <cristina.almaraz@gmail.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>