[PATCH] PR libstdc++/84654 Do not use __float128 if it is disabled by the compiler

[Marc Glisse]

On Thu, 1 Mar 2018, Tulio Magno Quites Machado Filho wrote:

> In order to use the __float128 in C++ it's necessary to check if
> it is supported in libstdc++ (i.e. via _GLIBCXX_USE_FLOAT128) and if the
> compiler enabled its support too, e.g. -mfloat128 or -mno-float128.

Shouldn't we ensure that _GLIBCXX_USE_FLOAT128 is undefined instead?

By the way, __FLOAT128__ is power-only. x86 has __SIZEOF_FLOAT128__ 
instead (why did power pick a different name?).

-- 
Marc Glisse