log4cpp: disable documentation build and install

We don't need the documentation on target.

Also fixes:
http://autobuild.buildroot.net/results/402/402587fe3ba9d537195ba470cf6f19f25ac246bf/
http://autobuild.buildroot.net/results/ea2/ea257496f51665b0a6b03f31e50744761c5d43da/
http://autobuild.buildroot.net/results/353/3533a32a7de7dae288558f43eb2b068081939e4d/

and many more.

Cc: Damien Lanson <damien@kal-host.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/log4cpp/log4cpp.mk

@@ -13,6 +13,7 @@ LOG4CPP_SUBDIR = log4cpp
 LOG4CPP_LICENSE = LGPLv2.1+
 LOG4CPP_LICENSE_FILES = log4cpp/COPYING
 LOG4CPP_INSTALL_STAGING = YES
+LOG4CPP_CONF_OPTS = --enable-doxygen=no --enable-dot=no
 
 # The default <pkg>_CONFIG_SCRIPTS handling does not apply
 define LOG4CPP_STAGING_CONFIG_SCRIPT_FIXUP