Use most recent/portable versions of LevelDB and Snappy dependencies

[ghost]

Currently the most recent version of leveldb-sys crate that we use for disk buffers depends on LevelDB 1.18. The latest upstream release of LevelDB is 1.22 (changelog).

In particular, version 1.21 added native Windows support, which could be very useful for #880.

Also, as mentioned in #1054, the version 1.1.2 of Snappy used by leveldb-sys has an Autotools-based build scripts, which make it less flexible about cross-compilation (in particular, a special flag has to be passed to the configure script, and levelb-sys build script doesn't support passing it). The most recent version 1.1.7 of Snappy supports CMake, which supports reading of build configuration from environment variables, so updating it could have simplified building for ARM.

Thus, it would be helpful to have an updated version of leveldb-sys crate supporting most recent versions of LevelDB and Snappy in order to support more targets.

[LucioFranco]

Just to note the author of leveldb has offered to give us access to the repo and apply these changes so that we are not blocked.

[binarylogic]

It sounds like we should definitely do this.

@LucioFranco can you have him give us access? Is there any we didn't take him up on that?

[LucioFranco]

@binarylogic I say let us discuss this more on Monday but I was not sure if we wanted to take up more work with leveldb yet so I wanted to have a discussion with the rest of the team before we commit to something like this. If we agree I will shoot an email over to the author.

[binarylogic]

What is the alternative? I do not want to block this issue to move off of leveldb. Moving off of leveldb will likely be a larger project addressed in https://github.com/timberio/vector/milestone/23; it is not something I want to rush or do haphazardly.

[binarylogic]

@a-rodin just documenting a discussion in Slack. We'd like to fork the leveldb-sys repo for now and make the changes. We will get the team added as contributors so that we have commit rights to the repo.

[ghost]

Note that we need to add CMake to list of our development requirements with this upgrade, as newer versions of LevelDB use it as the build system.

[ghost]

I think that for now we can keep the same version of leveldb-sys crate to not require everyone to install CMake, but use updated leveldb crate from our fork which can be compiled on ARM.