package/pkg-generic: handle host-tar as an extract dependency

package/pkg-generic: handle host-tar as an extract dependency

This moves the host-tar dependency handling from
DEPENDENCY_HOST_PREREQ to an extract dependency.

To achieve that, check-host-tar.mk fills in the
BR2_TAR_HOST_DEPENDENCY variable with host-tar if building a host-tar
is needed. The name BR2_TAR_HOST_DEPENDENCY has been chosen because it
matches the name BR2_CMAKE_HOST_DEPENDENCY already used in
check-host-cmake.mk.

The BR2_TAR_HOST_DEPENDENCY is added to all packages, except host-tar
itself (obviously) and host-skeleton, because we depend on
host-skeleton to install host-tar properly in HOST_DIR.

In addition, we modify tar.mk to explicitly build host-tar without
ccache: since ccache source code is available as a tarball, ccache
will obviously depend on host-tar if the system tar is insufficient.

Finally, to make things really clean, we also add
$(BR2_TAR_HOST_DEPENDENCY) to the dependencies of the tar filesystem
format, since it requires tar, so we'd better make sure we have a
suitable tar.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Tested-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>