zeromq: disable documentation

If asciidoc and xmlto are around it will automatically enable the
documentation build which is pointless.
Build time on i5-3330 with docs = 37s, without docs 25s.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/zeromq/zeromq.mk

@@ -8,6 +8,7 @@ ZEROMQ_VERSION = 4.1.5
 ZEROMQ_SITE = https://github.com/zeromq/zeromq4-1/releases/download/v$(ZEROMQ_VERSION)
 ZEROMQ_INSTALL_STAGING = YES
 ZEROMQ_DEPENDENCIES = util-linux
+ZEROMQ_CONF_OPTS = --without-documentation
 ZEROMQ_LICENSE = LGPLv3+ with exceptions
 ZEROMQ_LICENSE_FILES = COPYING COPYING.LESSER
 # For 0001-acinclude.m4-make-kernel-specific-flags-cacheable.patch