barrier: pick up new commit to fix compilation

This fixes #170103. Details about the compilation error are in the
issue. In brief, a header that used to be inferred now needs to be
explicitly added.

pkgs/applications/misc/barrier/default.nix

@@ -1,6 +1,7 @@
 { lib, fetchFromGitHub, cmake, curl, xorg, avahi, qtbase, mkDerivation,
   openssl, wrapGAppsHook,
-  avahiWithLibdnssdCompat ? avahi.override { withLibdnssdCompat = true; }
+  avahiWithLibdnssdCompat ? avahi.override { withLibdnssdCompat = true; },
+  fetchpatch
 }:
 
 mkDerivation rec {
@@ -15,6 +16,16 @@ mkDerivation rec {
     fetchSubmodules = true;
   };
 
+  patches = [
+    # This patch can be removed when a new version of barrier (greater than 2.4.0)
+    # is released, which will contain this commit.
+    (fetchpatch {
+      name = "add-missing-cstddef-header.patch";
+      url = "https://github.com/debauchee/barrier/commit/4b12265ae5d324b942698a3177e1d8b1749414d7.patch";
+      sha256 = "sha256-ajMxP7szBFi4h8cMT3qswfa3k/QiJ1FGI3q9fkCFQQk=";
+    })
+  ];
+
   buildInputs = [ curl xorg.libX11 xorg.libXext xorg.libXtst avahiWithLibdnssdCompat qtbase ];
   nativeBuildInputs = [ cmake wrapGAppsHook ];