ci: Add ccache 4.9.1

This commit adds the ccache v4.9.1, the latest version at the moment, to
the CI Docker image because the distro ccache package is relatively
outdated and does not support newer features used by the zephyr-runner
v2 (mainly, redis remote storage backend).

Note that the upstream ccache project does not distribute pre-compiled
AArch64 binary -- for AArch64, the distro-provided ccache package will
be used.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

Dockerfile.ci

@@ -7,6 +7,8 @@ ARG ZSDK_VERSION=0.16.5-1
 ENV ZSDK_VERSION=$ZSDK_VERSION
 ARG KITWARE_NINJA_VERSION=1.11.1.g95dee.kitware.jobserver-1
 ENV KITWARE_NINJA_VERSION=$KITWARE_NINJA_VERSION
+ARG CCACHE_VERSION=4.9.1
+ENV CCACHE_VERSION=$CCACHE_VERSION
 ARG DOXYGEN_VERSION=1.9.4
 ENV DOXYGEN_VERSION=$DOXYGEN_VERSION
 ARG RENODE_VERSION=1.14.0
@@ -38,6 +40,15 @@ RUN if [ "${HOSTTYPE}" = "x86_64" ]; then \
 	rm ninja-${KITWARE_NINJA_VERSION}_x86_64-linux-gnu.tar.gz \
 	; fi
 
+# Install ccache
+# NOTE: Pre-built ccache binaries are only available for x86_64 host.
+RUN if [ "${HOSTTYPE}" = "x86_64" ]; then \
+	wget ${WGET_ARGS} https://github.com/ccache/ccache/releases/download/v${CCACHE_VERSION}/ccache-${CCACHE_VERSION}-linux-x86_64.tar.xz && \
+	tar xf ccache-${CCACHE_VERSION}-linux-x86_64.tar.xz -C /opt && \
+	ln -s /opt/ccache-${CCACHE_VERSION}-linux-x86_64/ccache /usr/local/bin && \
+	rm ccache-${CCACHE_VERSION}-linux-x86_64.tar.xz \
+	; fi
+
 # Install Doxygen (x86 only)
 # NOTE: Pre-built Doxygen binaries are only available for x86_64 host.
 RUN if [ "${HOSTTYPE}" = "x86_64" ]; then \