[RFC PATCH] Optionally use -mlong-double-128 by default on {powerpc{,64},s390{,x},sparc,alpha}-linux

[Benjamin Kosnik]

> If we could use "g" for TFmode long double on the architectures in question
> (powerpc*-*-linux*, sparc{,v7,v8,v9}-*-linux*, s390*-*-linux* and
> alpha*-*-linux*), I'm all for that.  It would certainly help a lot for
> coexistence of C++ code with different long doubles in one app
> (of course you still can't call a long double referencing routine/method/etc.
> between differently built objects/libraries, but if C++ library A uses
> TFmode long double internally and not on its public interfaces and
> C++ library B uses DFmode long double internally, things still ought to work
> correctly and when you try to call void foo (long double); between
> differently built objects, you'd even get link time errors).
> And it would certainly simplify the libstdc++ patch a lot as well
> and make it easier to prove that it works correctly with both "e"
> and "g" long double.

I like this idea as well: it would remove some of the fragileness
around the current approach and make the 128 long double uses
unambiguous.

It makes this whole transition much simpler.

-benjamin