Backport emscripten 3.1.10 for deterministic builds

flake.lock

@@ -31,6 +31,22 @@
         "type": "github"
       }
     },
+    "nixpkgs-emscripten": {
+      "locked": {
+        "lastModified": 1652377891,
+        "narHash": "sha256-voVwmhzYFUKo4y98ZF7ZiKnku1ga1nRbbJEeXd0EKKE=",
+        "owner": "duxovni",
+        "repo": "nixpkgs",
+        "rev": "7f75c03d0af88e5de5ead83a90484fd20512d35e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "duxovni",
+        "ref": "emscripten",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "npmlock2nix": {
       "flake": false,
       "locked": {
@@ -51,6 +67,7 @@
       "inputs": {
         "flake-utils": "flake-utils",
         "nixpkgs": "nixpkgs",
+        "nixpkgs-emscripten": "nixpkgs-emscripten",
         "npmlock2nix": "npmlock2nix"
       }
     }

flake.nix

@@ -2,6 +2,7 @@
   description = "An implementation of the Double Ratchet cryptographic ratchet";
 
   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  inputs.nixpkgs-emscripten.url = "github:duxovni/nixpkgs/emscripten";
   # We can't use the current stable release because of
   # https://github.com/emscripten-core/emscripten/issues/14995
   inputs.flake-utils.url = "github:numtide/flake-utils";
@@ -10,7 +11,7 @@
     flake = false;
   };
 
-  outputs = { self, nixpkgs, flake-utils, npmlock2nix }:
+  outputs = { self, nixpkgs, nixpkgs-emscripten, flake-utils, npmlock2nix }:
    (
       flake-utils.lib.eachDefaultSystem (system:
         let
@@ -19,6 +20,7 @@
             overlays = [
               (final: prev: {
                 npmlock2nix = final.callPackage npmlock2nix {};
+                inherit (import nixpkgs-emscripten { inherit (prev) system config; }) emscripten;
               })
             ];
           };