44f5ae3eec
This commit extracts some MIR-related code from `common.py` and `update_mir_test_checks.py` into a dedicated `mir.py` module to improve code organization. This is a preparation step for https://github.com/llvm/llvm-project/pull/164965 and also moves some pieces already moved by https://github.com/llvm/llvm-project/pull/140296 All code intentionally moved verbatim with minimal necessary adaptations: * `log()` calls converted to `print(..., file=sys.stderr)` at `mir.py` lines 62, 64 due to a `log` locality.