Configure: correct the check of env vars vs command line flags

The check to detect if env / make variables conflicted with compiler /
linker flags on the configure command line went a little too far, and
would stop the configuration process if any such command line flag was
given, with no regard for the env / make variables at all.

This change refines the check so the stop only gets triggered if any
such flags were given AND any of the corresponding variables are set.

Reviewed-by: Andy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5561)