libxl: idl: support new "private" type attribute
This provides for fields in libxl datatypes which are only present in
the C version of structures and are used only by libxl itself. This
is useful when a libxl datatype wants to contain fields which are used
by libxl internally and which are only present in the structure to
avoid additional memory allocation inconvenience.
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>