man pages aren't installed when building 9.17.x

This has been reported by a customer, and I've been able to duplicate the behavior on my system (MacBook Pro M1). There have been reported ways to get the man pages to build (using sphinx-build, or running make doc), but I was unable to get either of these to work. I was finally able to build and install manpages by descending into doc/man at the source root and running make and make install there.