[gn build] Port 18df9d2

Author: llvmgnsyncbot

llvm/utils/gn/secondary/libcxx/include/BUILD.gn

@@ -608,6 +608,7 @@ if (current_toolchain == default_toolchain) {
       "__memory/allocator_arg_t.h",
       "__memory/allocator_destructor.h",
       "__memory/allocator_traits.h",
+      "__memory/array_cookie.h",
       "__memory/assume_aligned.h",
       "__memory/auto_ptr.h",
       "__memory/builtin_new_allocator.h",