urbackup-client: fix gcc-13 build failure

Without the change build fails on` master as
https://hydra.nixos.org/build/249116447:

    blockalign_src/crc.cpp: In function 'bool cryptopp_crc::IsAlignedOn(const void*, unsigned int)':
    blockalign_src/crc.cpp:191:23: error: 'uintptr_t' does not name a type
      191 |                 const uintptr_t x = reinterpret_cast<uintptr_t>(ptr);
          |                       ^~~~~~~~~

pkgs/applications/backup/urbackup-client/default.nix

@@ -15,6 +15,13 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-n0/NVClZz6ANgEdPCtdZxsEvllIl32vwDjC2nq5R8Z4=";
   };
 
+  postPatch = ''
+    find | fgrep crc.cpp
+    # Fix gcc-13 build failures due to missing includes
+    sed -e '1i #include <cstdint>' -i \
+      blockalign_src/crc.cpp
+  '';
+
   buildInputs = [
     wxGTK32
     zlib