Re: expand-before-require bug

[Paolo Bonzini]

>   - macros defined with AC_DEFUN_IDEMPOTENT are *known* to be expandable
>     any number of times, hence they may be both invoked and required,
> 
>   - macros defined with AC_DEFUN_ONCE are *known* to be expandable only
>     once, hence the recommendation for them is to AC_REQUIRE them,

Do we have any of these?  I'd just change AC_DEFUN_ONCE to the meaning
you suggest for AC_DEFUN_IDEMPOTENT, with this further change to its
semantics: if an AC_DEFUN_ONCE is invoked from the toplevel, never warn;
if it is invoked from a macro without AC_REQUIRE, always warn.  For 2.65
we can start using AC_DEFUN_ONCE more liberally in autoconf itself

Paolo