libllcp: ensure graphviz isn't used to generate documentation

We don't need the documentation, so it is a waste of time - And more
importantly, the .dot file isn't compatible with all graphviz versions
breaking the build.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libllcp/libllcp.mk

@@ -13,5 +13,7 @@ LIBLLCP_AUTORECONF = YES
 LIBLLCP_INSTALL_STAGING = YES
 LIBLLCP_LICENSE = GPLv3+
 LIBLLCP_LICENSE_FILES = COPYING
+# ensure graphviz isn't used
+LIBLLCP_CONF_ENV = ac_cv_path_DOT=
 
 $(eval $(autotools-package))