Update chainerx_cc/chainerx/backprop_mode.h
Update chainerx_cc/chainerx/backprop_mode.h

Co-Authored-By: hvy <a5848102d8491b6959f66fb5d5231fc8bd6a56a0@gmail.com>
niboshi/chainer,okuta/chainer,wkentaro/chainer,hvy/chainer,wkentaro/chainer,tkerola/chainer,chainer/chainer,hvy/chainer,wkentaro/chainer,hvy/chainer,wkentaro/chainer,keisuke-umezawa/chainer,niboshi/chainer,okuta/chainer,keisuke-umezawa/chainer,niboshi/chainer,keisuke-umezawa/chainer,chainer/chainer,okuta/chainer,okuta/chainer,chainer/chainer,hvy/chainer,chainer/chainer,pfnet/chainer,keisuke-umezawa/chainer,niboshi/chainer