feat: Move packaging scripts into dist/ and consolidate the service files

dist/nix/pkgs/main/cross-compilation-env.nix

@@ -0,0 +1,83 @@
+{ lib
+, pkgsBuildHost
+, rust
+, stdenv
+}:
+
+lib.optionalAttrs stdenv.hostPlatform.isStatic
+  {
+    ROCKSDB_STATIC = "";
+  }
+//
+{
+  CARGO_BUILD_RUSTFLAGS =
+    lib.concatStringsSep
+      " "
+      (lib.optionals
+        stdenv.hostPlatform.isStatic
+        [ "-C" "relocation-model=static" ]
+      ++ lib.optionals
+        (stdenv.buildPlatform.config != stdenv.hostPlatform.config)
+        [
+          "-l"
+          "c"
+
+          "-l"
+          "stdc++"
+
+          "-L"
+          "${stdenv.cc.cc.lib}/${stdenv.hostPlatform.config}/lib"
+        ]
+      );
+}
+
+  # What follows is stolen from [here][0]. Its purpose is to properly
+  # configure compilers and linkers for various stages of the build, and
+  # even covers the case of build scripts that need native code compiled and
+  # run on the build platform (I think).
+  #
+  # [0]: https://github.com/NixOS/nixpkgs/blob/nixpkgs-unstable/pkgs/build-support/rust/lib/default.nix#L48-L68
+  //
+(
+  let
+    inherit (rust.lib) envVars;
+  in
+  lib.optionalAttrs
+    (stdenv.targetPlatform.rust.rustcTarget
+    != stdenv.hostPlatform.rust.rustcTarget)
+    (
+      let
+        inherit (stdenv.targetPlatform.rust) cargoEnvVarTarget;
+      in
+      {
+        "CC_${cargoEnvVarTarget}" = envVars.ccForTarget;
+        "CXX_${cargoEnvVarTarget}" = envVars.cxxForTarget;
+        "CARGO_TARGET_${cargoEnvVarTarget}_LINKER" = envVars.ccForTarget;
+      }
+    )
+  //
+  (
+    let
+      inherit (stdenv.hostPlatform.rust) cargoEnvVarTarget rustcTarget;
+    in
+    {
+      "CC_${cargoEnvVarTarget}" = envVars.ccForHost;
+      "CXX_${cargoEnvVarTarget}" = envVars.cxxForHost;
+      "CARGO_TARGET_${cargoEnvVarTarget}_LINKER" = envVars.ccForHost;
+      CARGO_BUILD_TARGET = rustcTarget;
+    }
+  )
+  //
+  (
+    let
+      inherit (stdenv.buildPlatform.rust) cargoEnvVarTarget;
+    in
+    {
+      "CC_${cargoEnvVarTarget}" = envVars.ccForBuild;
+      "CXX_${cargoEnvVarTarget}" = envVars.cxxForBuild;
+      "CARGO_TARGET_${cargoEnvVarTarget}_LINKER" = envVars.ccForBuild;
+      HOST_CC = "${pkgsBuildHost.stdenv.cc}/bin/cc";
+      HOST_CXX = "${pkgsBuildHost.stdenv.cc}/bin/c++";
+    }
+  )
+)