Log Message:
devel/ccache: Build man page

The man page was lost in the update, due to needing asciidoctor.
However, it built (and thus caused a PLIST error) on machines with
asciidoctor installed.  Depend on asciidoctor, rather than forcing it
off, since this package ought to have a man page.

Tested on NetBSD 9 amd64.