package/qlibc: fix musl build by removing usage of internal glibc header sys/cdefs.h

package/qlibc: fix musl build by removing usage of internal glibc header sys/cdefs.h

Fixes
http://autobuild.buildroot.net/results/15c/15ce460214875c2e56d5d26372778b43cd7325ad/
http://autobuild.buildroot.net/results/790/79098fb27ef2d5b09df777cd7365a61d6de55c52/
http://autobuild.buildroot.net/results/8d3/8d3dad2dcf5b3c7fa94cc759386759b1ac9e3287/
http://autobuild.buildroot.net/results/9d8/9d8f6259c62e15cc528ec99d6375cc02c2bc7489/
http://autobuild.buildroot.net/results/a05/a0540ed23bd2d48cd742aa1b0228719b13e162b6/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>