musl: work around gcc 4.9.x bug

MUSL doesn't build happily with gcc 4.9.0/1 so work around the bug when
appropiate as suggested by upstream.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>