xfsprogs: missing and dummy calls for OS X support

xfsprogs: missing and dummy calls for OS X support

Add and update various API, macros and types where is some change
in OS X or xfsprogs. Most changes are in darwin.h.

Add dummy implementations where native support is nonexistent
and the tools are not expected to work anyway, so all tools can be
at least compiled.

Signed-off-by: Jan Tulak <jtulak@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>