[Bug libstdc++/124268] `import std` initializer symbol is not shipped in `libstdc++`

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124268

--- Comment #16 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Patrick Palka from comment #15)
> Another approach might be to downgrade the "exporting internal linkage
> entity" error into a pedwarn. Nathaniel, do you reckon it'd be feasible to
> gracefully handle this situation (i.e. so that the export is still usable by
> importers)?

Or even not export the names with internal linkage. If somebody complains that
feclearexcept is not present in module std on FreeBSD, we can point them to the
FreeBSD bug report.

So a "just ignore exports that can't be exported" option.