libxc: Add unsafe decompressors

libxc: Add unsafe decompressors

Add decompressors based on hypervisor code.  This are used in mini-os by
pv-grub.

This enables pv-grub to boot kernels compressed with e.g. xz, which are
becoming more common.

Signed-off-by: Bastian Blank <waldi@debian.org>
Adjusted to use terminology "unsafe" rather than "trusted" to indicate
that the user had better sanitise the data (or not care, as in stub
domains) as suggested by Tim Deegan. This was effectively a sed script.

Minimise the changes to hypervisor code by moving the "compat layer" into the
relevant libxc source files (which include the Xen ones).

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>