libgnurx: output libgnurx.a when static

pkgs/os-specific/windows/libgnurx/default.nix

···
     sha256 = "0xjxcxgws3bblybw5zsp9a4naz2v5bs1k3mk8dw00ggc0vwbfivi";
   };
 
+  # file looks for libgnurx.a when compiling statically
+  postInstall = lib.optionalString stdenv.hostPlatform.isStatic ''
+    ln -s $out/lib/libgnurx{.dll.a,.a}
+  '';
+
   meta = {
     platforms = lib.platforms.windows;
   };