Configure: fix the version string in the configure output

Since `$config{version}` and `$config{version_num}` were removed
in commit 3a63dbef

, the configure output displays an empty
version number string in parentheses instead of the version number.

This pull request fixes that by adding new config variables
`version` and `full_version`, analogous to `OPENSSL_VERSION_STR`
and `OPENSSL_FULL_VERSION_STR`.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7841)