[libc++] Fix use of std::errc() for C++ < 11 (#138522)
After 8fc2538f338088bd084d217a7569d72c3b630e8c "Reapply '[libc++]
Optimize num_put integral functions' (#131613) (#133572)", including
<locale> in C++03 mode with Debug hardening enabled fails.
This patch fixes that by applying a workaround used elsewhere to
construct errc in C++03 mode.
