Use prebuilt LLVM

Dockerfile

@@ -1,13 +1,6 @@
-FROM ubuntu:24.04
-
+FROM silkeh/clang:20
 WORKDIR /build
-RUN apt update -y
-RUN apt install -y cmake curl wget cppcheck
-
-RUN wget https://apt.llvm.org/llvm.sh && \
-    chmod +x llvm.sh && \
-    ./llvm.sh 20
-
+RUN apt update -y && apt install -y cppcheck
 ADD runchecks.sh /entrypoint.sh
 COPY . .
 RUN chmod +x /entrypoint.sh