NetBSD doesn't have setresuid(). introcuce libxl__setresuid(),
which on NetBSD assert() that it's never called (it should not be called when
dm restriction is off, and NetBSD doesn't support dm restriction at
this time).
On linux and FreeBSD it just calls setresuid().
Signed-off-by: Manuel Bouyer <bouyer@netbsd.org>
Reviewed-by: Ian Jackson <ian.jackson@eu.citrix.com>
