Do not shell out on 5.14.0 and up if perl provides internals (Nicholas)

Do not shell out on 5.14.0 and up if perl provides internals (Nicholas)

Nicholas applied 996978124d77fbe8 in remotes/origin/nicholas/configpm:

Config::Perl::V::myconfig can avoid `$^X -V` on 5.14.0 and later.

On 5.14.0 and later the Config module has subroutines that provide
all the data contained within perl -V, so there's no need to shell
out to $^X to get it.

Also add a test that forces Config::Perl::V::myconfig to shell out,
to check consistency between the two approaches.