* support control flow

* supoort sync_parameters_buffers

* fix the bug of sparse embedding

* new group

* ci compatible fix

* assert nccl

* [ROCM] update fluid imperative for rocm (part1), test=develop

* [ROCM] update reducer.cc after merge, test=develop

* update reducer cmake after merge, test=develop

* use iwyu clean include second time, test=develop

* fix fleet for multi-stream

* fix memcpy for ncclid

* use sync to solve move operation

* add reducer

* refine envent for memorycopy

* add concat&split for allreduce

* apply concat & split for fuse tensor

* fix nccl dep

* fix the untest, compile problem and ddp initialize problem

* fix untest for mac & add some comments & solve the repeated param in sublayers

* fix untest for windows & fix document

* add retry for dygraph parallel socket bind

* change to loop always

* fix writing error

* nccl init support hostname and ip; test=develop

* refine err msg

* follow comments

* add new macro BOOST_GET_SAFELY & unittests, test=develop

* add different macro type, test=develop

* fix get macro type in executor, test=develop

* four macro part change backup

* using one macro for all case, test=develop

* revert attribute change, test=develop

* change to three func to solve gcc4.8 bug, test=develop

* polish some details, test=develop

initialize global nccl context in dygraph
test=develop

cmake选项中添加了WITH_NCCL，显示指定是否编译NCCL的部分代码，WITH_NCCL默认打开，但如果WITH_GPU为OFF，则关闭WITH_NCCL

添加了PADDLE_WITH_NCCL定义

单机单卡能够关闭NCCL编译，多卡的话需要默认打开NCCL，如果关闭NCCL，则只能使用单卡
Co-authored-by: N石晓伟 <39303645+Shixiaowei02@users.noreply.github.com>

test=develop

test=develop

add NCCLParallelContext for parallel dygraph