Support building RocksDB with jemalloc

[akrylysov]

RocksDB includes some optimizations when it's compiled with jemalloc. This PR allows enabling jemalloc using new jemalloc feature.

[aleksuss]

Overall looks good. But I'd recommend to add a check of this feature to Github Actions CI.

[aleksuss]

Warning: "jemalloc support for x86_64-pc-windows-msvc is untested"

As I can see jemalloc doesn't support x86_64-pc-windows-msvc target.

[akrylysov]

Thanks for taking a look. I converted the PR to a draft for now until I can figure out the best way to handle Windows.

[akrylysov]

I tried using the x86_64-pc-windows-gnu target on Windows (the default target is x86_64-pc-windows-msvc), but unfortunately jemalloc fails to compile as well. I disabled jemalloc tests on Windows.

Non-glibc allocator is a must-have for RocksDB on Linux in production. Here is more details on switching to jemalloc http://smalldatum.blogspot.com/2018/04/myrocks-malloc-and-fragmentation-strong.html or other alternative allocator https://blog.cloudflare.com/the-effect-of-switching-to-tcmalloc-on-rocksdb-memory-use/.

Note: clippy failing on the CI is unrelated to this PR. It's due to a new Rust release.

[aleksuss]

PR #547 resolve clippy warings.

[akrylysov]

I'm not sure why the CI fails now, GitHub Actions doesn't show any error output 😕

[aleksuss]

Probably, there was something wrong with CI. I restarted jobs and it's ok now.