untie: fix build with gcc14

- add patch that adds `#define _GNU_SOURCE` to `untie.c`, as glibc
wrapper over clone syscall is not declared otherwise.
Fixes `-Wimplicit-function-declaration` error:
```
untie.c:411:15: error: implicit declaration of function 'clone';
did you mean 'close'? []
  411 |         ret = clone(child_process, &stack[STACK_SIZE - 1], flags, &args_info);
      |               ^~~~~
      |               close
make: *** [<builtin>: untie.o] Error 1
```

pkgs/by-name/un/untie/add-define-gnu-source.patch

@@ -0,0 +1,12 @@
+diff --git a/untie.c b/untie.c
+index f08a10d..d3d20b4 100644
+--- a/untie.c
++++ b/untie.c
+@@ -18,6 +18,7 @@
+  * Copyright (c) 2006, 2007 Guillaume Chazarain <guichaz@yahoo.fr>
+  */
+ 
++#define _GNU_SOURCE
+ #include <sys/time.h>
+ #include <sys/resource.h>
+ #include <sys/wait.h>

pkgs/by-name/un/untie/package.nix

@@ -12,6 +12,11 @@ stdenv.mkDerivation rec {
     sha256 = "1334ngvbi4arcch462mzi5vxvxck4sy1nf0m58116d9xmx83ak0m";
   };
 
+  patches = [
+    # fix build with gcc14
+    ./add-define-gnu-source.patch
+  ];
+
   makeFlags = [ "PREFIX=$(out)" ];
 
   meta = with lib; {