zeromq: needs NPTL

The recent zeromq version bump to 4.2.5 added a call to
pthread_condattr_setclock() which is only provided by the NPTL
implementation of pthreads. Add this dependency to zeromq and all
reverse dependencies recursively.

Fixes:
http://autobuild.buildroot.net/results/2d0/2d070074097270a1e6973bc19e2bded2a7023c49/
http://autobuild.buildroot.net/results/1ce/1ce6d6f0f6390f552954a09f7dc753e0baa86675/
http://autobuild.buildroot.net/results/97c/97c5b9f3bc2c94f8476e884b9a3163bbf2dad8d4/



Cc: Asaf Kahlon <asafka7@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>