Makefile.PL: use AutoConf before trying to exec

[rehsack]

Instead of requiring hacking Makefile.PL by packagers like happening in

• https://github.com/meta-cpan/meta-cpan/tree/master/recipes-security/net-ssleay-perl/net-ssleay-perl
• http://git.openembedded.org/meta-openembedded/tree/meta-perl/recipes-perl/libnet/libnet-ssleay-perl use Config::AutoConf when available.

This patch shall give the new maintainers of Net::SSLeay an insight how it could look like - a full flavoured check is implemented in Unix::Statgrab.

Finally, Config::AutoConf should be mentioned in meta->prereqs->config->suggests (or recommends).

@moto-timo: any additional suggestions?

Signed-off-by: Jens Rehsack [email protected]