[Bug libstdc++/67932] Incorrect conversion to hexfloat

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67932
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Libstdc++ has no implementation of printf, so ::printf and std::printf are
exactly the same function, with std::printf defined as:

namespace std
{
  using ::printf;
}