Make `TORCH_CUDA_ARCH_LIST` as an environment variable (#167)

* Add 10.0 to TORCH_CUDA_ARCH_LIST
Signed-off-by: Guyue Huang <guyueh@nvidia.com>

* Revert csrc/CMakeLists change; in setup.py make TORCH_CUDA_ARCH_LIST configurable
Signed-off-by: Guyue Huang <guyueh@nvidia.com>

---------
Signed-off-by: Guyue Huang <guyueh@nvidia.com>

setup.py

@@ -10,7 +10,8 @@ if __name__ == '__main__':
     print(f'NVSHMEM directory: {nvshmem_dir}')
 
     # TODO: currently, we only support Hopper architecture, we may add Ampere support later
-    os.environ['TORCH_CUDA_ARCH_LIST'] = '9.0'
+    if os.getenv('TORCH_CUDA_ARCH_LIST', None) is None:
+        os.environ['TORCH_CUDA_ARCH_LIST'] = '9.0'
     cxx_flags = ['-O3', '-Wno-deprecated-declarations', '-Wno-unused-variable',
                  '-Wno-sign-compare', '-Wno-reorder', '-Wno-attributes']
     nvcc_flags = ['-O3', '-Xcompiler', '-O3', '-rdc=true', '--ptxas-options=--register-usage-level=10']