Switch to new rocksdb with some hacks to resolve linking errors

Rocksdb and `wasmtime-environ` both link `zstd`. In the final link step,
this leads to linking errors because of duplicate symbols. The linked
Rocksdb fixes this by using `zstd-sys` as well. However, this currently
also requires modifications in `zstd-sys`. Someone will need to come up
with a better implementation.