cmake: Add BUILD_CUDA option not to build CUDA intentionally
cmake: Add BUILD_CUDA option not to build CUDA intentionally

okuta/chainer,chainer/chainer,wkentaro/chainer,okuta/chainer,jnishi/chainer,jnishi/chainer,okuta/chainer,jnishi/chainer,pfnet/chainer,ktnyt/chainer,tkerola/chainer,niboshi/chainer,keisuke-umezawa/chainer,hvy/chainer,niboshi/chainer,ktnyt/chainer,jnishi/chainer,chainer/chainer,chainer/chainer,niboshi/chainer,wkentaro/chainer,keisuke-umezawa/chainer,hvy/chainer,ktnyt/chainer,hvy/chainer,wkentaro/chainer,wkentaro/chainer,hvy/chainer,chainer/chainer,niboshi/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,okuta/chainer,ktnyt/chainer