[CI]Install clang in dokerfile for triton ascend (#4409)

### What this PR does / why we need it?
Install clang in dokerfile for triton ascend

- vLLM version: v0.13.0
- vLLM main:
d68209402d

Signed-off-by: Meihan-chen <jcccx.cmh@gmail.com>

Dockerfile.a3

@@ -63,6 +63,14 @@ RUN export PIP_EXTRA_INDEX_URL=https://mirrors.huaweicloud.com/ascend/repos/pypi
     python3 -m pip install -v -e /vllm-workspace/vllm-ascend/ --extra-index https://download.pytorch.org/whl/cpu/ && \
     python3 -m pip cache purge
 
+# Install clang-15 (for triton-ascend)
+RUN apt-get update -y && \
+    apt-get -y install clang-15 && \
+    update-alternatives --install /usr/bin/clang clang /usr/bin/clang-15 20 && \
+    update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-15 20 && \
+    rm -rf /var/cache/apt/* && \
+    rm -rf /var/lib/apt/lists/*
+
 # Install modelscope (for fast download) and ray (for multinode)
 RUN python3 -m pip install modelscope 'ray>=2.47.1,<=2.48.0' 'protobuf>3.20.0' && \
     python3 -m pip cache purge