unix2winchr
code = unix2winchr(&un, &unlen, 0, pmp);
code = unix2winchr(&un, &unlen, 0, pmp);
code = unix2winchr(&un, &unlen, 0, pmp);
c1 = unix2winchr(__DECONST(const u_char **, &np), &len,
c2 = unix2winchr(&un, &unlen, LCASE_BASE, pmp);
static uint16_t unix2winchr(const u_char **, size_t *, int, struct msdosfsmount *);