ABI baselines, --enable-clocale choices, and that AC_TRY_RUN test

[Benjamin Kosnik]

> As a result, __c_locale gets typedef'd to int* rather than __locale_struct*,
> and the i686 baseline symbols file contains, e.g.,
> 
>     _ZNSt10moneypunctIcLb0EEC1EP15__locale_structPKcj
> 
> whereas mine has
> 
>     _ZNSt10moneypunctIcLb0EEC1EPiPKcj

Yes. The different locale models will change this typedef. I don't see
any way around this.

> (I'm trying a build now on another system that should be able to support
> --enable-clocale=gnu, if it works I'll test the baseline stuff there first.)

Sounds good.

> Before I start renaming things, what are some of the common config options
> that changes the ABI /within/ a platform?  Loren's already found changes
> wrt to --enable-threads:
> 
>     http://gcc.gnu.org/ml/libstdc++/2002-08/msg00227.html
> 
> This is starting to sound like another multilibs-style mess:  for a given
> triplet, we have multiple combinations of commonly used --enables that
> each result in a different baseline_symbols.txt file.

Well. Most of these:

http://gcc.gnu.org/onlinedocs/libstdc++/configopts.html

-benjamin