Configure: print generic advice when dying

On the same note, change the 'NASM not found' message to give specific
advice on how to handle the failure.

Fixes #6765

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Andy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6771)