fix: Clean up temporary dir if it's left the default

fix: Clean up temporary dir if it's left the default

Cleanup of the temporary directory is done if it is $CCACHE_DIR/tmp,
which used to be the default until [1] where the default was changed to
/run/user/$UID/ccache-tmp. Improve this so that cleanup happens if the
temporary directory is equal to the default regardless of the default.

[1]: 213d9883a0c3944749f8512eeb784d8572ad8d91