package/xproto_inputproto: disable documentation

Resolves:
http://autobuild.buildroot.net/results/e6b/e6badde04047e10023b97946bbff434abc07344d/

Signed-off-by: Matthew Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/x11r7/xproto_inputproto/xproto_inputproto.mk

@@ -11,6 +11,7 @@ XPROTO_INPUTPROTO_LICENSE = MIT
 XPROTO_INPUTPROTO_LICENSE_FILES = COPYING
 XPROTO_INPUTPROTO_INSTALL_STAGING = YES
 XPROTO_INPUTPROTO_INSTALL_TARGET = NO
+XPROTO_INPUTPROTO_CONF_ENV = ac_cv_path_ASCIIDOC=""
 
 $(eval $(autotools-package))
 $(eval $(host-autotools-package))