Disable building C extensions when using target device sendnn (#34)

Upstream changes broke the logic to disable building the C extensions
when building for sendnn.

This was causing the following error when trying to pip install vllm
inside the [dev container
build](https://v3.travis.ibm.com/github/ai-foundation/aiu-inference-dev/builds/25651578).

This tiny fix resolves that.

Signed-off-by: Thomas Parnell <tpa@zurich.ibm.com>

Author: tdoublep

setup.py

@@ -286,7 +286,7 @@ def _build_custom_ops() -> bool:
 
 
 def _build_core_ext() -> bool:
-    return not (_is_neuron() or _is_tpu() or _is_openvino() or _is_xpu())
+    return not (_is_neuron() or _is_tpu() or _is_openvino() or _is_xpu() or _is_sendnn())
 
 
 def get_hipcc_rocm_version():