This is causing build failures in some build environments, like NixOS.
I don't think we are going to patch bdb at this point, and this warning
has existed for as long as we've used bdb.
Fixes #25211.
Tested (in Docker) with:
```bash
docker run -it nixos/nix
nix-shell -p gitMinimal gcc12 libtool pkg-config curl gnumake patch autoconf automake
git clone https://github.com/bitcoin/bitcoin
make -C bitcoin/depends bdb
```
Co-authored-by: Ryan Ofsky <ryan@ofsky.org>
b46c6ec52e