This arg caused gmake install on OpenIndiana 2019.10 (illumos) fail with:
install: The -c, -f, -n options each require a directory following! install: The -c, -f, -n options each require a directory following! install: The -c, -f, -n options each require a directory following! gmake[1]: *** [Makefile:41: install] Error 2 gmake[1]: Leaving directory '/usr/local/share/mercurial/doc'
The workaround is to run gmake install-bin.
The man page for 10.14 says this is to copy the file and is only for
compatability, as it is the default. The CentOS 7 man page says it is ignored.
The top level makefile doesn't use this argument at all, so I'm not sure why
it's here.