fix homeless-shelter error

flake.nix

@@ -202,11 +202,20 @@
           fast-servo/linien-fast-servo-server.patch
         ];
         nativeBuildInputs = [
-          (pkgs.python3.withPackages(ps: [ migen misoc ps.linien-common ]))
+          (pkgs.python3.withPackages(ps: [
+            migen misoc
+            (ps.linien-common.overrideAttrs(oa: {
+              # config.py tries to access $HOME, but we do not need it for building gateware
+              postPatch = ''
+                echo > linien_common/config.py
+                echo > linien_common/__init__.py
+              '';
+              doCheck = false;
+              }))
+            ]))
           vivado
         ];
         buildPhase = ''
-          export HOME=$(mktemp -d)
           python -m gateware.fpga_image_helper -p fastservo
         '';
         installPhase = ''