[gn build] Port 3a63407

Author: llvmgnsyncbot

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

@@ -277,7 +277,6 @@ if (current_toolchain == default_toolchain) {
       "__assert",
       "__atomic/aliases.h",
       "__atomic/atomic.h",
-      "__atomic/atomic_base.h",
       "__atomic/atomic_flag.h",
       "__atomic/atomic_init.h",
       "__atomic/atomic_lock_free.h",