[Libguestfs] [PATCH nbdkit v2 follow-up 0/4] Miscellaneous fixes

Follow-up to this patch: https://listman.redhat.com/archives/libguestfs/2021-November/msg00251.html Patches 1-3 are probably down to over-active warnings in the old version of GCC. Patch 3 in particular is bogus, but needed to get around the warning. Patch 4 moves the test so it's next to the header file being tested. I don't mind if you squash these into your patch before pushing. Rich.