Add ccache (#85)

This change adds `ccache` to the Debian, Ubuntu, and RHEL images, so our
CI pipelines can take advantage of caching (once configured to do so).

Note that due to our use of the UBI images of RHEL, the `ccache` package
cannot be installed using the default repositories available through the
package manager. I first tried installing it by pulling it from from
GitHub, however that required installing an appropriate versioning for
each RHEL distro as otherwise GLIBC incompatibilities would surface.
Instead, I added the RHEL version-specific Fedora EPEL repository, which
is a project that provides RHEL-compatible packages, as that will
install a compatible `ccache` version.

To get a better view of which version is installed of which package,
including `ccache`, they are now printed together at the end of each
base image. This also acts as a sanity-check that the packages are
actually installed.

Author: bthomee

docker/debian/Dockerfile

@@ -40,6 +40,7 @@ RUN <<EOF
 pkgs=()
 pkgs+=(ca-certificates) # Enable TLS verification for HTTPS connections by providing trusted root certificates.
 pkgs+=(binutils-gold)   # Required build tool.
+pkgs+=(ccache)          # Optional build tool for caching build artifacts.
 pkgs+=(curl)            # Dependency for tools requiring downloading data.
 pkgs+=(dpkg-dev)        # Required packaging tool.
 pkgs+=(debhelper)       # Required packaging tool.
@@ -62,8 +63,6 @@ apt-get clean
 rm -rf /var/lib/apt/lists/*
 EOF
 
-RUN ld.gold --version
-
 # Install Python-based tools and cmake.
 ARG CONAN_VERSION
 ARG GCOVR_VERSION
@@ -85,7 +84,17 @@ ARCH=$(uname -m)
 wget -O mold.tar.gz https://github.com/rui314/mold/releases/download/v${MOLD_VERSION}/mold-${MOLD_VERSION}-${ARCH}-linux.tar.gz
 tar -xzf mold.tar.gz --strip-components=1 -C /usr/local
 rm mold.tar.gz
+EOF
+
+# Print versions.
+RUN <<EOF
+ccache --version
+cmake --version
+conan --version
+gcovr --version
+ld.gold --version
 mold --version
+python3 --version
 EOF
 
 # ====================== GCC IMAGE ======================

docker/rhel/Dockerfile

@@ -10,6 +10,15 @@ ENTRYPOINT ["/bin/bash"]
 # This is not inherited from the base image.
 ARG RHEL_VERSION
 
+# Install the Fedora Extra Packages for Enterprise Linux (EPEL) repository,
+# which provides additional packages for RHEL and CentOS Stream, some of which
+# we want to install.
+RUN <<EOF
+dnf install -y --setopt=tsflags=nodocs https://dl.fedoraproject.org/pub/epel/epel-release-latest-${RHEL_VERSION}.noarch.rpm
+dnf clean -y all
+rm -rf /var/cache/dnf/*
+EOF
+
 # Install tools that are shared by all stages.
 RUN <<EOF
 pkgs=()
@@ -19,6 +28,7 @@ if [ "${RHEL_VERSION}" -eq "8" ]; then
 else
   pkgs+=(binutils-gold)   # Required build tool.
 fi
+pkgs+=(ccache)            # Optional build tool for caching build artifacts.
 pkgs+=(file)              # Required packaging tool.
 pkgs+=(git)               # Required build tool.
 pkgs+=(gpg)               # Dependency for tools requiring signing or encrypting/decrypting.
@@ -67,8 +77,6 @@ mkdir -p /usr/local/lib
 ln -sf /usr/lib/python3.12 /usr/local/lib/python3.12
 EOF
 
-RUN ld.gold --version
-
 # Install Python-based tools and cmake.
 ARG CONAN_VERSION
 ARG GCOVR_VERSION
@@ -90,7 +98,17 @@ ARCH=$(uname -m)
 wget -O mold.tar.gz https://github.com/rui314/mold/releases/download/v${MOLD_VERSION}/mold-${MOLD_VERSION}-${ARCH}-linux.tar.gz
 tar -xzf mold.tar.gz --strip-components=1 -C /usr/local
 rm mold.tar.gz
+EOF
+
+# Print versions.
+RUN <<EOF
+ccache --version
+cmake --version
+conan --version
+gcovr --version
+ld.gold --version
 mold --version
+python3 --version
 EOF
 
 # ====================== GCC IMAGE ======================

docker/ubuntu/Dockerfile

@@ -27,6 +27,7 @@ RUN <<EOF
 pkgs=()
 pkgs+=(ca-certificates) # Enable TLS verification for HTTPS connections by providing trusted root certificates.
 pkgs+=(binutils-gold)   # Required build tool.
+pkgs+=(ccache)          # Optional build tool for caching build artifacts.
 pkgs+=(curl)            # Dependency for tools requiring downloading data.
 pkgs+=(dpkg-dev)        # Required packaging tool.
 pkgs+=(file)            # Required packaging tool.
@@ -48,8 +49,6 @@ apt-get clean
 rm -rf /var/lib/apt/lists/*
 EOF
 
-RUN ld.gold --version
-
 # Install Python-based tools and cmake.
 ARG CONAN_VERSION
 ARG GCOVR_VERSION
@@ -71,7 +70,17 @@ ARCH=$(uname -m)
 wget -O mold.tar.gz https://github.com/rui314/mold/releases/download/v${MOLD_VERSION}/mold-${MOLD_VERSION}-${ARCH}-linux.tar.gz
 tar -xzf mold.tar.gz --strip-components=1 -C /usr/local
 rm mold.tar.gz
+EOF
+
+# Print versions.
+RUN <<EOF
+ccache --version
+cmake --version
+conan --version
+gcovr --version
+ld.gold --version
 mold --version
+python3 --version
 EOF
 
 # ====================== GCC IMAGE ======================