Re: [v3] default to --disable-long-long, ctype fixes

[Benjamin Kosnik <bkoz at redhat dot com>]

Right. Sorry if I was so abrupt before.

Here are the gory details for linux:

This is basically a "C" header issue, as far as I'm concerned. The only 
way to get definitions like 'lldiv_t' out of stdlib.h is to pass 
_GNU_SOURCE. As this option is not passed by default, ISO-C9X features 
are turned off when a user does something like "#include <stdlib.h>" and 
then compiles like "g++ foo.cc"

That case has to work.

The problem comes in where libstdc++-v3 explicitly enables ISO-C99 
features in config/os/gnu-linux/bits/os_defines.h -- this is used during 
configure to probe and see what kind of ISO-C99 support is around: on 
linux, as _GNU_SOURCE is explicitly defined, lldiv_t is found in 
stdlib.h, so HAVE_LLDIV_T is defined. This makes sense. The problem is 
when a user does something like

#include <stdlib.h>
#include <cstdlib>

and compiles like "g++ foo.cc"

What happens: stdlib.h is parsed without ISO-C99  features, then cstdlib 
is parsed, expecting ISO-C99 features from stdlib.h, including things like 
lldiv_t. This is incorrect, and results in a compile-time failure. This is bad.

Other heades are also show similar symptoms.

Does this make it easier to understand why it's off by default? I agree, 
it would be nice to have it on by default. However, I don't see how 
that's possible, given the current state of C99 support in the "C" library.

Ulrich, feel free to correct me if I'm way off base.

-benjamin