xprompt: fix build with gcc 14 (#394030)

pkgs/by-name/xp/xprompt/package.nix

@@ -30,11 +30,16 @@ stdenv.mkDerivation rec {
   ];
 
   postPatch =
-    let
-      configFile =
-        if lib.isDerivation conf || builtins.isPath conf then conf else writeText "config.h" conf;
-    in
-    lib.optionalString (conf != null) "cp ${configFile} config.h";
+    ''
+      sed -i "8i #include <time.h>" xprompt.c
+    ''
+    + (
+      let
+        configFile =
+          if lib.isDerivation conf || builtins.isPath conf then conf else writeText "config.h" conf;
+      in
+      lib.optionalString (conf != null) "cp ${configFile} config.h"
+    );
 
   makeFlags = [
     "CC:=$(CC)"