Make 'with_fallback' use 'use' instead of 'require'

This enables us to require module versions, and to fall back to a
bundled version if the system version is too low.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6682)

(cherry picked from commit e9bc5706)