There are several libraries here, somewhat overlapping:

libxc: C library for use with both Xinu and standalone libraries
	for printf, scanf, etc.  Uses putc and getc for all i/o.
	Written in pre-ANSI C, Sun/Gnu as.
libsa: library for downloaded standalone programs--implements putc
	and getc, also startup, etc.
	Written in pre-ANSI C, Sun/Gnu as.
gnulib: Gnu cc support library, so that it can be compiled for 68000/
	68010 rather than the host's CPU.
	Written in pre-ANSI C, should be compiled with cc, not gcc.
libsa_on7300: combo of libsa and libxc for use on the ATT7300 running
	UNIX, to build SA programs such as Tutor
	Written in pre-ANSI C, ATT7300 as.
tutor_on7300: debugger/downloader to be built on ATT7300 running UNIX,
	written to floppy disk, booted from host
	Written in ANSI C, ATT7300 as.

