Some of the features affect nix dependencies, so we need to have a
full feature list available when constructing the nix derivation. This
incidentally fixes the bug where we weren't enabling jemalloc on rocksdb
in CI/devshells, because jemalloc is now a default feature. It does not
fix the more general class of that issue, where CI is performing an
`--all-features` build in a nix devshell built for default-features.
I am now passing `--no-default-features` to cargo, and having it use our
unified feature list rather than duplicating the unification inside cargo.
Without setting JEMALLOC_OVERRIDE, we end up linking to two different
jemalloc builds. Once dynamically, as a transitive dependency through
rocksdb, and a second time to the static jemalloc that tikv-jemalloc-sys
builds.
Some of the improvements here include:
* rocksdb can actually use jemalloc now instead of just pulling in a
second rocksdb for no reason
* "complement-runtime" factored back out into shell file
* complement image no longer uses `mkDerivation` for `copyToRoot`
because that's what `buildEnv` is for
* complement image no longer sets `SERVER_NAME`, complement already does
that
* all packages were factored out into `callPackage`-able files for use
with a custom `lib.makeScope pkgs.newScope`
* new version of `mkPackage` has options that are easier to use and
override such as `features`
