libkcapi: disable documentation

Disable db2pdf, db2ps and xmlto which are used for building PDF, PS, man
or html documentation

Fixes:
 - http://autobuild.buildroot.org/results/28df3b50d90bc53b965280b77224f89fe09ec2b9

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 8b3dea2c2a0434fae4824cfe3098b93e684979ba)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libkcapi/libkcapi.mk

@@ -11,6 +11,10 @@ LIBKCAPI_AUTORECONF = YES
 LIBKCAPI_INSTALL_STAGING = YES
 LIBKCAPI_LICENSE = BSD-3-Clause (library), BSD-3-Clause or GPL-2.0 (programs)
 LIBKCAPI_LICENSE_FILES = COPYING COPYING.gplv2 COPYING.bsd
+LIBKCAPI_CONF_ENV = \
+	ac_cv_path_DB2PDF="" \
+	ac_cv_path_DB2PS="" \
+	ac_cv_path_XMLTO=""
 
 ifeq ($(BR2_PACKAGE_LIBKCAPI_APPS),y)
 LIBKCAPI_CONF_OPTS += \