apache2: fix libtool's path in apxs

libtool-cross recipe install it as ${HOST_SYS}-libtool

Signed-off-by: Kirill Esipov <yesipov@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
(cherry picked from commit 33f5a5b43dff271a04b885a74232dcd66b9644fe)
Signed-off-by: Armin Kuster <akuster808@gmail.com>