bdwgc: fix static build

Fixes:
http://autobuild.buildroot.net/results/6d3/6d3f73f7b5e4e7bd1293aae9b626f38ac456b6c4/
http://autobuild.buildroot.net/results/1ba/1ba511c629f724eee8b75b9b34fe8db154b3cfe1/
http://autobuild.buildroot.net/results/a54/a54cc1bdc5dcb4c459cfbcae3368811e2170d100/



and more.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>