setjmp as macro

[Paul Rabin]

ANSI C (4.1.6) says that except where otherwise specified, all library
routines must be implemented as functions; additional macro
implementations are permissible, but these must behave like functions.
In particular, macro implementations of library functions must
evaluate their arguments exactly once.

In 4.6, setjmp is "otherwise specified": setjmp may be implemented as
either a macro or a function.  Conforming applications may not
assume either that a function is defined or that a function is not
defined.

My question:

	Does ANSI C require that a macro implementation of setjmp
	evaluate its arguments exactly once?  If so, do you have a
	suggestion for handling the jmp_buf argument?  

Thanks!

	-Paul Rabin