The `<time.h>` functions `asctime`, `gmtime`, `mktime` and their `_r`
variants are purely computational functions which convert between well
defined time representations and/or strings. There's no reason these
shouldn't be available in bare-metal builds of the library as well as
hosted ones: even if the library has no way to find out the time in
POSIX format, it might still see POSIX-style `time_t` values in input
data (e.g. network protocols) and need to interpret them.
The only obstacle to this was that the `out_of_range()` helper function
set `errno` to `EOVERFLOW`, which fails in a bare-metal build because
the extra POSIX error values aren't defined, including `EOVERFLOW`. So
I've made that assignment conditional on `EOVERFLOW` being defined.
Fixes#85556.
efd71d9213