I'm ready to import libxo-2.3.0 into freebsd and want review comments.

This diff is massive (220KLOD); you might have an easier time looking at the source on https://github.com/Juniper/libxo.git

Highlights in this delta include:

• llvm plugins:
  • "validate": validate libxo format strings during compilation, generating errors and warnings
  • "precompile": compile format strings into binary data, avoiding run-time parsing of format strings
• "--libxo filter=XXX" allows filtering of output using an xpath-like syntax
• "rtoon" is a variant of "toon, allowing a reduction in tokens when feeding data to LLMs
• support for FreeBSD's exterr infra in xo_err* functions

rtoon is an dynamically loader encoder; the filter module is also dynamically loader when needed

libxo contains an extensive test library. In addition, the libxo-enabled binaries are exersized by kyua.