Enable algorithm filtering

[baentsch]

Fixes #1331

• [ No] Does this PR change the input/output behaviour of a cryptographic algorithm (i.e., does it change known answer test values)? (If so, a version bump will be required from x.y.z to x.(y+1).0.)
• Does this PR change the the list of algorithms available -- either adding, removing, or renaming? Does this PR otherwise change an API? (If so, PRs in oqs-provider, OQS-OpenSSL, OQS-BoringSSL, and OQS-OpenSSH will also need to be ready for review and merge by the time this is merged.)

[baentsch]

@dstebila FYI, additional testing incl. AppVeyor/Windows added as discussed yesterday, so this is now ready from my side.

[dstebila]

Code looks good to me. But if we're going to change the default compilation behaviour to omit some algorithms, then I think that should also update README.md to indicate this.

[baentsch]

Code looks good to me. But if we're going to change the default compilation behaviour to omit some algorithms, then I think that should also update README.md to indicate this.

So done in 4eb3567

[baentsch]

Just re-considered the implications of merging this: Downstream projects must be prepared for the potential reduction of algorithms supported (or if no optimized build for some downstream projects are desired, must build liboqs with the "All/experimental algs" setting). So this PR shall not be merged before those PRs are available.

[baentsch]

Oops -- comment in the wrong window :-( Disregard. One more thought: Please add an explicit statement that "sntrup761" is only included until it is not needed for interop testing any more. The statement that it shall be removed if broken already is implicit in the language at https://github.com/open-quantum-safe/liboqs#limitations-and-security -- so maybe it might be suitable to add the "needed-for-interop" statement also there. Agreed, @dstebila ?
Finally, please feel free to add yourself to https://github.com/open-quantum-safe/liboqs/blob/main/CONTRIBUTORS, @ryndia

[baentsch]

Thanks @dstebila for marking the conversation resolved. For some reason, there's still a blocking "Changes requested" marker, though... Did I overlook something?