dockerfile: Install a newer version of CMake

This is required if building the master version of LLVM, past the
11 release branch.

Dockerfile.cross

@@ -16,13 +16,6 @@ RUN apt-get update -qq && \
     apt-get clean -y && \
     rm -rf /var/lib/apt/lists/*
 
-RUN cd /opt && \
-    wget https://github.com/Kitware/CMake/releases/download/v3.16.2/cmake-3.16.2-Linux-x86_64.tar.gz && \
-    tar -zxvf cmake-*.tar.gz && \
-    rm cmake-*.tar.gz && \
-    mv cmake-* cmake
-ENV PATH=/opt/cmake/bin:$PATH
-
 ARG CROSS_ARCH=x86_64
 ENV CROSS_TOOLCHAIN_PREFIX=/opt/llvm-mingw-$CROSS_ARCH