libxo-2.2.0

Major features:

• Add "rtoon" encoder
  • rtoon is an AI-friendly format that minimizes token count, inspired by toon, but streaming friendly

Code management:

• Add support for macos-tahoe (llvm-21)
• Support "cc -v" in xocc so FreeBSD can determine COMPILER_TYPE
  • add a fake "clang" option
• add "dense" flag (XOF_DENSE and XFF_DENSE)
• configure: add check for missing "clang" package in macports
• add encoder version check/fail
• avoid "const" in constant expressions (a gnu extension that clang now complains about)
• deprecate old "whiteboard" concept in encoders