The default installation settings of xdm match those used for most platforms
in the previous X.Org releases:

Scripts & modules:	$(libdir)/X11/xdm (aka $(prefix)/lib/X11/xdm)
Configuration files:	$(libdir)/X11/xdm
Pixmap files:		$(libdir)/X11/xdm/pixmaps
Log files:		/var/log
Process id/lock files:	/var/run

These may be overridden with the following options to configure:
Loadable modules:	--with-xdmlibdir
Scripts:		--with-xdmscriptdir (or --with-xdmlibdir)
Configuration files:	--with-xdmconfigdir (or --with-xdmlibdir)
Pixmap files:		--with-xdmpixmapdir (or --with-xdmlibdir)
Log files:		--with-logdir
Process id/lock files:	--with-piddir

For instance, some packagers/sites may prefer:
	--with-xdmconfigdir=/etc/X11/xdm --with-xdmlibdir=$(prefix)/lib/xdm
	--with-xdmscriptdir=/etc/X11/xdm