libxc: use multicall for memory-op on Linux (and Solaris)

libxc: use multicall for memory-op on Linux (and Solaris)

Some sub-functions, XENMEM_maximum_gpfn and XENMEM_maximum_ram_page in
particular, can return values requiring more than 31 bits to represent.
Hence we cannot issue the hypercall directly when the return value of
ioctl() is used to propagate this value. This is the case for Linux
and Solaris (and hence needs changing), while the BSDs avoid using the
return value for dual purposes altogether, and MiniOS already wraps all
hypercalls in a multicall.

Suggested-by: Jürgen Groß <jgross@suse.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Jackson <iwj@xenproject.org>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>