bug#70036: 30.0.50; Move file-truename to the C level

[Po Lu]

Theodor Thornhill <theo@thornhill.no> writes:

> OK - for my education on the portability argument. Is that because of
> Emacs support targets like haiku and old versions of windows, or
> something else inherent in these functions?

Haiku supports realpath, but not wordexp.  We must reimplement virtually
all POSIX functions of this nature on Windows, as the versions provided
by system C libraries, if they exist at all, are inadequate for some
reason or another.  Furthermore, these functions are absent from a
number of other operating systems, such as OpenBSD and Android 14.0, and
on others (Alpine, I believe) wordexp is severely inefficient for being
implemented as a wrapper around /bin/sh.