Standardized predefined CPP symbols, down with folklore

[David Canzi]

In addition to documenting these predefined symbols, the symbols themselves
ought to be chosen so that they are not likely to be accidentally used as
variables in somebody's program.  Around here, "unix" and "waterloo" are
predefined, and who knows what else is?  If predefined symbols were all to
begin and end with underscore characters, and this fact were documented,
then nobody would fall into the trap of inadvertently using one.