[gn build] Port 42ba740

Author: llvmgnsyncbot

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

@@ -294,6 +294,7 @@ if (current_toolchain == default_toolchain) {
       "__atomic/atomic_flag.h",
       "__atomic/atomic_init.h",
       "__atomic/atomic_lock_free.h",
+      "__atomic/atomic_ref.h",
       "__atomic/atomic_sync.h",
       "__atomic/check_memory_order.h",
       "__atomic/contention_t.h",
@@ -302,6 +303,7 @@ if (current_toolchain == default_toolchain) {
       "__atomic/is_always_lock_free.h",
       "__atomic/kill_dependency.h",
       "__atomic/memory_order.h",
+      "__atomic/to_gcc_order.h",
       "__availability",
       "__bit/bit_cast.h",
       "__bit/bit_ceil.h",