nccl/rccl integration

[seagater]

Use dlopen to load nccl/rccl apis from shared library to replace Fallback code for Allgather, Allreduce, Broadcast, ReduceScatter.

Add two related environment variables
-x MSCCLPP_ENABLE_SHARED_LIB=TRUE -x MSCCLPP_NCCL_LIB_PATH=path_to_libnccl.so/librccl.so

[SreevatsaAnantharamu]

Additional symbols that need to be loaded from libnccl.so:

• ncclGetUniqueId
• ncclCommInitRank

nccl_ops_t->ncclGetUniqueId(

Here, before returning, you have to call nccl_ops_t->ncclCommInitRank and create a new real NCCL's communicator. Inside MSCCL++'s ncclComm_t, you can have a void * or ncclComm_t nccl_comm.

nccl_ops_t->ncclCommInitRank(&commPtr->nccl_comm, ... )

[seagater]

Add two related environment variables:
-x MSCCLPP_ENABLE_SHARED_LIB=TRUE -x MSCCLPP_NCCL_LIB_PATH=path_to_libnccl.so/librccl.so

Support dlopen for following nccl apis:
ncclCommInitRank
ncclGetUniqueId
ncclCommDestroy
ncclCommUserRank
ncclAllGather
ncclAllReduce
ncclBroadcast

Pass following tests
nccl-test:
Allgather, Allreduce, Broadcast, ReduceScatter

rccl-test:
Allgather, Allreduce, Broadcast, ReduceScatter