Create version #defines

[baentsch]

Currently, AFAIK there is no simple library version define that a downstream could utilize to adapt to API changes in liboqs: The only define there is is "OQS_VERSION_TEXT" and I'm not sure that's making it sufficiently easy to adapt a downstream's code to liboqs capabilities: The goal of (and one purpose for) oqsprovider is to build against all versions of liboqs, so a simple-to-use code-level library version test facility should be there, e.g. similar to what we have in openssl. Worthwhile a separate issue/PR or simple enough to do as part of this PR? If the latter, the corresponding oqsprovider update could be done as a "-tracker" update as this is an API-changing PR (either way).

Originally posted by @baentsch in #1919 (comment)