This directory contains only those headers that require specific magic
to work right with the EDG front end.  For the rest, you need only
what's required in the C and C++ standards.

In the definition of stddef.h, a good version of offsetof is:

#define offsetof(t, memb) ((size_t)__INTADDR__(&(((t *)0)->memb)))

It uses an EDG extension (__INTADDR__) to perform the otherwise nonstandard
conversion from pointer to integer.  This is not a requirement, but it does
avoid spurious warnings when the header is compiled in strict mode.

The C99 tgmath.h header can be implemented fairly easily by using the
EDG extension pseudo-macro __generic.  See its description in the
External Interface chapter of the internal documentation.
