Starting with Python 3.11, the definition HAVE_LIBB2 was introduced to support building the _blake2 extension against the libb2 library.

See python/cpython@b16b6bb8dac ("bpo-47095: Use libb2 to provide blake2 implementation (GH-32059)", 2022-03-26)

In additional of building against the built-in implementation, the CMake build-system should be updated to support this.

Related issues and pull requests:

• Add support for Python 3.10, 3.11, 3.12 and 3.13 #350
• Add support for building Python 3.11.x #387