fix multiple definition while building evoformer (microsoft#4556)

Current builder for evoformer use the same name for `attention.cpp` and
`attention.cu`, leading to same intermediate filename `attention.o`:
```shell
march=nocona -mtune=haswell -ftree-vectorize -fPIC -fstack-protector-strong -fno-plt -O2 -ffunction-sections -pipe -
isystem /home/zejianxie/.conda/envs/dll/include -DNDEBUG -D_FORTIFY_SOURCE=2 -O2 -isystem 
/home/zejianxie/.conda/envs/dll/include build/temp.linux-x86_64-cpython-
310/csrc/deepspeed4science/evoformer_attn/attention.o build/temp.linux-x86_64-cpython-
310/csrc/deepspeed4science/evoformer_attn/attention.o build/temp.linux-x86_64-cpython-
310/csrc/deepspeed4science/evoformer_attn/attention_back.o
```
and
```
`attention_impl(at::Tensor&, at::Tensor&, at::Tensor&, at::Tensor&, at::Tensor&, at::Tensor&, at::Tensor&)':
      tmpxft_0012bef1_00000000-6_attention.compute_86.cudafe1.cpp:(.text+0x330): multiple definition of `attention_impl(at::Tensor&, at::Tensor&, at::Tensor&, at::Tensor&, at::Tensor&, at::Tensor&, at::Tensor&)'; build/temp.linux-x86_64-cpython-310/csrc/deepspeed4science/evoformer_attn/attention.o:tmpxft_0012bef1_00000000-6_attention.compute_86.cudafe1.cpp:(.text+0x330): first defined here
      /home/zejianxie/.conda/envs/dll/bin/../lib/gcc/x86_64-conda-linux-gnu/11.4.0/../../../../x86_64-conda-linux-gnu/bin/ld: build/temp.linux-x86_64-cpython-310/csrc/deepspeed4science/evoformer_attn/attention.o:(.bss+0x0): multiple definition of `torch::autograd::(anonymous namespace)::graph_task_id'; build/temp.linux-x86_64-cpython-310/csrc/deepspeed4science/evoformer_attn/attention.o:(.bss+0x0): first defined here
```

I use following to reproduce and confirm my fix works:
```
git clone https://github.com/NVIDIA/cutlass --depth 1
CUTLASS_PATH=$PWD/cutlass DS_BUILD_EVOFORMER_ATTN=1 pip install ./DeepSpeed --global-option="build_ext"
```

![image](https://github.com/microsoft/DeepSpeed/assets/41792945/9e406b37-330c-431c-8bf9-6be378dee4ff)

Co-authored-by: Conglong Li <[email protected]>

op_builder/evoformer_attn.py

@@ -27,7 +27,7 @@ def extra_ldflags(self):
 
     def sources(self):
         src_dir = 'csrc/deepspeed4science/evoformer_attn'
-        return [f'{src_dir}/attention.cpp', f'{src_dir}/attention_back.cu', f'{src_dir}/attention.cu']
+        return [f'{src_dir}/attention.cpp', f'{src_dir}/attention_back.cu', f'{src_dir}/attention_cu.cu']
 
     def nvcc_args(self):
         args = super().nvcc_args()