Explicitly set WINEARCH.

default.nix

@@ -164,6 +164,7 @@ let
     #new prefix for any changes. Needs fast prefix installs and state outside.
       uuid=$(basename $(${pkgs.nix}/bin/nix path-info "$(readlink -f $BASH_SOURCE)"))
       export WINEPREFIX="${prefixBaseDir}/$uuid"
+      export WINEARCH=win64
 
     #export all global env vars
       ${lib.concatMapStrings (x: "export " + x + "\n") (wineGlobalEnv