test/zdtm: fix compilation of maps02.c when MADV_DONTDUMP is unknown

Error was:
maps02.c: In function ‘main’:
maps02.c:57:74: error: ‘MADV_DONTDUMP’ undeclared (first use in this function)
maps02.c:57:74: note: each undeclared identifier is reported only once for each function it appears in
make: *** [maps02] Error 1
ERROR: fail to start /home/root/criu/test/zdtm/live/static/maps02

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>