{buildNpmPackage,node-gyp}: fix cross builds (#387729)

pkgs/build-support/node/build-npm-package/default.nix

···
       # Stripping takes way too long with the amount of files required by a typical Node.js project.
       dontStrip = args.dontStrip or true;
 
+      env = {
+        npm_config_arch =
+          {
+            "x86_64" = "x64";
+            "aarch64" = "arm64";
+          }
+          .${stdenv.hostPlatform.parsed.cpu.name} or stdenv.hostPlatform.parsed.cpu.name;
+        npm_config_platform = stdenv.hostPlatform.parsed.kernel.name;
+      } // (args.env or { });
+
       meta = (args.meta or { }) // {
         platforms = args.meta.platforms or nodejs.meta.platforms;
       };

pkgs/by-name/no/node-gyp/package.nix

···
 {
+  stdenv,
   buildNpmPackage,
   fetchFromGitHub,
   lib,
···
 
   postPatch = ''
     ln -s ${./package-lock.json} package-lock.json
+    substituteInPlace gyp/pylib/gyp/**.py --replace-fail sys.platform '"${stdenv.targetPlatform.parsed.kernel.name}"'
   '';
 
   dontNpmBuild = true;