buildroot

memcached: fix musl build

Add a patch fixing pre-processor warnings that breaks the build. The patch is
pending upstream.

Fixes:

 http://autobuild.buildroot.org/results/ee9bdcad1c2d392558812c5ec185e92c20ed5340/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>