vpnc: use nativeperl to run perl scripts

inhert perlnative and make sure we use nativeperl
to run perl scripts when compile.

fixed:
| ./makeman.pl
| Can't locate Fatal.pm in @INC

Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>