whether get_pointer_safety returns
pointer_safety::relaxed or
pointer_safety::preferred if the implementation has relaxed pointer safety, [util.dynamic.safety]
whether locale object is global or per-thread, [locale]
whether sequence pointers are copied by basic_filebuf move
constructor, [filebuf.cons]
whether sequence pointers are copied by basic_stringbuf move
constructor, [stringbuf.cons]
whether source of translation units must
be available to locate template definitions, [lex.phases]
whether stack is unwound before calling std::terminate()
when a noexcept specification
is violated, [except.terminate]