enable silent build output by default

enable silent build output by default

Enable the automake feature to produce silent output by default.
When compiling code, we now see things like:
$ make
  CC       addgrps.o
  CC       age.o
  CC       audit_help.o
...

This can be disabled via configure's --disable-silent-rules or
by passing V=1 to make.

Custom output (like in the man subdirs) don't (yet) respect this
feature.  More work will be needed to clean those up.