libcaca: fix build on Darwin (#347014)

pkgs/by-name/li/libcaca/package.nix

@@ -39,6 +39,10 @@ stdenv.mkDerivation rec {
 
   configureFlags = [
     (if x11Support then "--enable-x11" else "--disable-x11")
+  ] ++ lib.optionals stdenv.hostPlatform.isDarwin [
+    # Suppresses a build failure building Cocoa support due to accessing private ivar `_running`,
+    # which no longer available.
+    (lib.enableFeature false "cocoa")
   ];
 
   env.NIX_CFLAGS_COMPILE = lib.optionalString (!x11Support) "-DX_DISPLAY_MISSING";