Scylla's coding standard requires that each header is self-sufficient,
i.e., it includes whatever other headers it needs - so it can be included
without having to include any other header before it.
We have a test for this, "ninja dev-headers", but it isn't run very
frequently, and it turns out our code deviated from this requirement
in a few places. This patch fixes those places, and after it
"ninja dev-headers" succeeds again.
Fixes#10995
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes#10997
a7fa29bceb