[PATCH] libstdc++: Fix for non-constexpr math_errhandling

[Jonathan Wakely]

On Wed, 19 Jan 2022 at 08:10, Matthias Kretz wrote:

> Follow-up to my last patch. This one is a more thorough fix. Tested on
> x86_64-
> linux. OK for trunk?
>
> ---- 8< ----
>
> Use SFINAE magic to support: "It is unspecified whether math_errhandling
> is a macro or an identifier with external linkage." [C Standard]
>

The patch is OK for trunk, but I don't understand what the C standard means
here.

"the macro math_errhandling expands to [...]. It is unspecified whether
math_errhandling is a macro or an identifier with external linkage."

So is it a macro or not?