We want to make the header standalone so it includes all the stuff it
needs. However, including macro.h for assert_cc() doesn't work because
of generate-audit_type-list.sh which would have to become more complex
to handle the extra include directories.
Instead, let's just use _Static_assert() directly which is a builtin and
doesn't need any extra includes.
It's great that we provide fallback values, but if we got one of those wrong,
it could be a long time before anyone noticed. So let's add asserts that the
our internal defines actually match the official ones, when the latter are
available.
I did not add '#include "macro.h"' to missing_{audit,capability}, because
those are processed by an awk script that would need additional include
directories and could be confused by the additional lines. We don't include
those headers standalone anyway, so this is not necessary anyway.
