dependencies: check that a full perl installation is available

The host-autoconf build process requires a full Perl installation, or
at least a Perl installation that has the Data::Dumper module
installed. On a basic Debian system, only 'perl-base' is installed,
but Data::Dumper is in the 'perl' package.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>