* main.c (main): Set MAKE_TTYOUT and MAKE_TTYERR.

* configure.ac: Test for isatty() and ttyname()
* makeint.h: provide a substitute for ttyname() if it's not available.
* config.ami.template, config.h-vms.template, config.h.W32.template:
define/undefine HAVE_ISATTY/HAVE_TTYNAME macros.
* NEWS, doc/make.texi: Document these new variables.