gentoo: use FEATURES="ccache"

gentoo

@@ -4,18 +4,16 @@ FROM gentoo/stage3-amd64:latest
 COPY --from=portage /usr/portage /usr/portage
 
 ENV ACCEPT_KEYWORDS="amd64" \
-    CCACHE_DIR="/gentoo/ccache" \
     EMERGE_DEFAULT_OPTS="--jobs=9 --load-average=8 --with-bdeps=y" \
-    FEATURES="-sandbox -usersandbox" \
+    FEATURES="ccache -sandbox -usersandbox" \
+    CCACHE_SIZE="2G" \
     MAKEOPTS="-j9 -l8" \
-    PATH="/usr/lib/ccache/bin${PATH:+:}$PATH" \
     USE="cairo introspection jpeg tiff"
 
-RUN mkdir -p /gentoo/ccache \
+RUN emerge dev-util/ccache \
 &&  emerge app-text/poppler \
     dev-python/pycairo \
     dev-python/pygobject \
-    dev-util/ccache \
     media-libs/exiftool \
     media-libs/mutagen \
     sys-apps/bubblewrap \