syslog-ng: Link against librt

Some of the rabbit-mq tools need to link against librt, specify
LIBS=-lrt when configuring.

Fixes:
http://autobuild.buildroot.net/results/a3d/a3dfdebd76d47df11a8e26a215bb88fbce8dc6f7
http://autobuild.buildroot.net/results/7d2/7d26e8efe67bf958162a309acb20800e669543e4
http://autobuild.buildroot.net/results/7b5/7b5370d12a2ff8937cba3a201d4edce3dcd12a6e
http://autobuild.buildroot.net/results/bab/babbb089ce1a7750495323248f21402960fb6c80

Helped-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/syslog-ng/syslog-ng.mk

@@ -11,6 +11,8 @@ SYSLOG_NG_LICENSE = LGPLv2.1+ (syslog-ng core), GPLv2+ (modules)
 SYSLOG_NG_LICENSE_FILES = COPYING
 SYSLOG_NG_DEPENDENCIES = host-bison host-flex host-pkgconf \
 	eventlog libglib2 openssl pcre
+# rabbit-mq needs -lrt
+SYSLOG_NG_CONF_ENV = LIBS=-lrt
 SYSLOG_NG_CONF_OPTS = --disable-manpages
 SYSLOG_NG_PATCH = \
 	https://github.com/dnsjts/syslog-ng/commit/7b2b673ae2640ce9ad396f538fc25acb6e4405ec.patch \