[PATCH] libstdc++: implement locale support for AIX

[CHIGOT, CLEMENT]

> * There are minor formatting issues:
> 
>   Should the linebreak in the extern inline definitions of strtof_l be
>   after the return type, not before, matching GNU coding standards?  It
>   may well be that the C++ style is different, though.
> 
>  Unrelated whitespace changes in xpg7/ctype_members.cc

I haven't yet check all the format issues. Especially, because the previous
code was already wrongly formatted at some point. I'll do that when 
releasing a "final" version of the patch.

> * The changes in the copyright ranges need to be undone, given that this
>  is just a renamed/augmented version of the previous dragonfly code.

Ok, I wasn't sure about that. I'll revert. 

> * Seeing the __DragonFly__ || __FreeBSD__ again, I had a quick look at
>   the FreeBSD 12.2 headers and found that localeconv_l does take a
>   locale_t arg, just like uselocale.  DragonFlyBSD seems to be the same
>   according to their online manuals.  I expect to give the code a try in
>   a FreeBSD 12.2 VM at some point to check.

Actually, it seems that the problem isn't about input argument, but 
the output which should "int*".

> * While you now define _GLIBCXX_C_LOCALE_XPG7 in
>  config/locale/xpg7/c_locale.h, config/os/aix/ctype_configure_char.cc
>   still tests the previous _GLIBCXX_C_LOCALE_IEEE_2008.

Arf, I've missed that. it might not be the last patch then. 
(I've made so much versions of it as I've tried to backport it to our 
old versions. It seems that I've mixed up things...)