Crosstool allows to create toolchains for you. It can only create the initial toolchain for you. It will not compile other needed libraries or applications for you, it will not be able to track dependencies or to package them properly. OpenEmbedded supports all configurations crosstool supports. You can start to create toolchains with OpenEmbedded, then as your needs grow create a more complete SDK from already present base libraries and applications and if you recognize you need to have packages for the target you have them almost built already.