syslog-ng: disable mongodb

libbson is a dependency of the mongo-c-driver that syslog-ng uses. Buildroot
doesn't package mongo-c-driver so syslog-ng uses the bundled one. The bundled
mongo-c-driver in turn may optionally use a bundled libbson. When Buildroot
builds libbson mongo-c-driver detects that and does not configure its bundled
libbson. This breaks the build of the syslog-ng mongodb module because it adds
the bundled libbson to the headers search path.

Disable the mongodb module to avoid this issue.

Fixes:
http://autobuild.buildroot.net/results/843/84331e9a168d8bdf2cceca8e9e1480611c1ecaed/
http://autobuild.buildroot.net/results/b5b/b5bad64abbf5764faf2a7129a1a25ad75c34980b/
http://autobuild.buildroot.net/results/3c3/3c32f4eb7436da06f3fb59f928363959df2a5e86/

Cc: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/syslog-ng/syslog-ng.mk

@@ -13,7 +13,7 @@ SYSLOG_NG_DEPENDENCIES = host-bison host-flex host-pkgconf \
 # rabbit-mq needs -lrt
 SYSLOG_NG_CONF_ENV = LIBS=-lrt
 SYSLOG_NG_CONF_OPTS = --disable-manpages --localstatedir=/var/run \
-	--disable-java --disable-java-modules
+	--disable-java --disable-java-modules --disable-mongodb
 
 # We override busybox's S01logging init script
 ifeq ($(BR2_PACKAGE_BUSYBOX),y)