unify functions of mkldnn_fc and refine comments

Delete unused `USE_OP` in combination op

Fix Clang compile error

Host and device transform API

Cond_op with dynamic if-else checked-in

Fix enforce test failed and demangle stack info

Using LoDTensor instead of Tensor in every operator.

Add MKLDNNConvLayer

auto generate USE_OP() in pybind.cc

Note: If no symbol with a suitable value is found, both this field and dli_saddr shall be set to NULL.

Delete unused Op dependence in CMakeList

fix shape of output tensor of cross_entropy_op.

Fix unitest of pad_op