The de-facto pseudo-standard pre-define was "unix", not "__unix__";
ANSI rendered a pre-define of "unix" illegal (because it's part of the
application namespace); the GCC folks invented "__unix__" as a
workaround for this.

Given the enormous diversity of unix systems out there, it's not at
all clear what code can assume from "#ifdef unix" or "#ifdef __unix__";
the exact meaning is likely to be specific to a particular portable
software package, which is why it belongs in CFLAGS..

					- Bill