czmq: add patch to fix build issue with recent glibc

glibc 2.20 is now warning when _BSD_SOURCE is used (as it's replaced
by _DEFAULT_SOURCE), and czmq has the bad idea of forcing the usage of
-Werror, causing build issues with the recent NIOS II toolchain based
on glibc 2.20.

This commit adds a patch to czmq to fix that. The patch has been
submitted upstream.

Fixes:

  http://autobuild.buildroot.org/results/64a/64a7eef2155248146e7f3a55e85fe60bc5b67791/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>