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.
Using a enum is all nice and generic, but at this point it seems unlikely that
we'll add further build modes. But having an enum means that we need to include
the header file with the enumeration whenerever the conditional is used. I want
to use the conditional in log.h, which makes it hard to avoid circular imports.
There is little point in #defining and #undefining CAP_LAST_CAP multiple times.
The check is only done in developer mode. After all, it's not an error to
compile on a newer kernel, and we shouldn't even warn in that case.
