ccache: Build with ENABLE_DOCUMENTATION=OFF

ccache: Build with ENABLE_DOCUMENTATION=OFF

This adjusts the Makefile to use the new option to turn off the
doc builds. It will not cause any problems except a warning
about unused options if combined with a ccache source missing
the upstream patch.

Since a config setting is required to re-enable the doc build this
is equivalent to unconditionally disabling the docs if the config
setting is not created.

Signed-off-by: David Adair <djabhead@aol.com>
(cherry picked from commit 2d1546832357a3a8bd18680bd31dd92050e739b2)