libc-client: create empty libc-client package to satisfy deps of -dev one

Collected errors:
 * satisfy_dependencies_for: Cannot satisfy the following dependencies for packagegroup-core-standalone-hhvm-sdk-target:
 *      libc-client (= 2007e-r1) *

Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>