qapi: untie 'if' conditions from C preprocessor Hi, This series makes the 'if' conditions less liberal, by formalizing a simple expression tree based on bare boolean logic of configure option identifiers. (this will allow to express conditions in Rust in my QAPI-Rust PoC series, but it is worth a standalone post) This is based on John Snow QAPI cleanup branch: https://gitlab.com/jsnow/qemu/-/tree/python-qapi-cleanup-pt6 thanks v2: - fix the normalization step to handle recursive expr - replace IfCond by QAPISchemaIf (JohnS) - commit message and documentation tweaks - mypy/flake8/isort