Export.cpp files in seven libraries defined APS5_VABI exports that no
target compiled, and nothing noticed: tools/progress.py counts them from
the sources. check_test_registration.py, which CI runs after configure,
now also reads Ninja's compile commands and fails for every non-test .cpp
under core/libs/prx that defines an APS5_VABI function and is neither
compiled nor included by a compiled source.