[Bug c/70742] Support div as a builtin

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70742

--- Comment #12 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
A script that assumes build = host = target is obviously unacceptable.

You can't do any compilations for $target at all when configuring GCC, 
only when configuring its runtime libraries such as libgcc, because there 
may not be a pre-existing compiler for $target at all.  You can grep 
target headers if they are available at configure time, but that's all, 
and they may not be available.

I think you'd need to defer associating a declaration with a built-in 
function until after the declaration of div in a system header has been 
seen, at which point you have the header's declaration of div_t available 
(ISO C doesn't allow calling div without including the header that 
declares it).  This delayed declaration does of course make it different 
from all existing built-in functions.