pass pkgsCrossStatic to mkOciImage, not pkgsHost

This fixes a bug where the aarch64 OCI image had metadata saying it was
an x86_64 OCI image. On top of that, I think the metadata was actually
right (aside from Conduit's binary): since all other packages were being
pulled from `pkgsHost`, an OCI image cross compiled for aarch64 from a
different architecture would result in unexecutable binaries (e.g. tini)
since they were compiled for the completely wrong architecture.

from: https://gitlab.com/famedly/conduit/-/merge_requests/579

Signed-off-by: strawberry <strawberry@puppygock.gay>

.gitlab-ci.yml

@@ -68,6 +68,9 @@ static:aarch64-unknown-linux-musl:
     paths:
       - conduit
 
+# Note that although we have an `oci-image-x86_64-unknown-linux-musl` output,
+# we don't build it because it would be largely redundant to this one since it's
+# all containerized anyway.
 oci-image:x86_64-unknown-linux-gnu:
   stage: artifacts
   image: nixos/nix:2.19.2

flake.nix

@@ -183,33 +183,44 @@
     {
       packages = {
         default = package pkgsHost;
-
         oci-image = mkOciImage pkgsHost self.packages.${system}.default;
-
-        # Build an OCI image from the musl aarch64 build so we don't have to
-        # build for aarch64 twice (to make a gnu version specifically for the
-        # OCI image)
-        oci-image-aarch64-unknown-linux-musl = mkOciImage
-          pkgsHost
-          self.packages.${system}.static-aarch64-unknown-linux-musl;
-
-        # Don't build a musl x86_64 OCI image because that would be pointless.
-        # Just use the gnu one (i.e. `self.packages."x86_64-linux".oci-image`).
-      } // builtins.listToAttrs (
-        builtins.map
-          (crossSystem: {
-            name = "static-${crossSystem}";
-            value = package (import nixpkgs {
+      }
+      //
+      builtins.listToAttrs
+        (builtins.concatLists
+          (builtins.map
+            (crossSystem:
+              let
+                binaryName = "static-${crossSystem}";
+                pkgsCrossStatic =
+                  (import nixpkgs {
                     inherit system;
                     crossSystem = {
                       config = crossSystem;
                     };
                   }).pkgsStatic;
-          })
+              in
+              [
+                # An output for a statically-linked binary
+                {
+                  name = binaryName;
+                  value = package pkgsCrossStatic;
+                }
+
+                # An output for an OCI image based on that binary
+                {
+                  name = "oci-image-${crossSystem}";
+                  value = mkOciImage
+                    pkgsCrossStatic
+                    self.packages.${system}.${binaryName};
+                }
+              ]
+            )
             [
               "x86_64-unknown-linux-musl"
               "aarch64-unknown-linux-musl"
             ]
+          )
         );
 
       devShells.default = pkgsHost.mkShell {