The `wcsxfrm` function copies a wide character string into a buffer,
such that comparing the new string against any similarly pre-processed
string with `wcscmp` produces the same result as if the original strings
were compared with `wcscoll`.
Our current `wcscoll` implementation is simply an alias for `wcscmp`, so
`wcsxfrm` needs to perform no actions other than copying the string.
This function converts a single wide character into its multibyte
representation (UTF-8 in our case). It is called from libc++'s
`std::basic_ostream<wchar_t>::flush`, which gets called at program exit
from a global destructor in order to flush `std::wcout`.
A zero-initialized mbstate_t struct has to be a valid initial state, so
we can just zero-initialize it whenever we need to reset.
Having a helper function for resetting the struct might imply that you
can add additional setup operations afterwards, which is not the case.
wint_t is also not supposed to be defined by sys/types.h, but should
be defined in wchar.h instead. Since we require it for our definition of
btowc, let's move it to the correct place.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
