package/gdk-pixbuf: fix static build

Fix static build failure which is raised since the switch to
meson-package in commit a7b51ed3

Fixes:
 - http://autobuild.buildroot.org/results/6cd54c497f5d19342ec94ece713547b887e4c02d



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
[Arnout: add link to upstream MR]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>