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)