use cygwin functions to list windows volume roots as `\0`-delimited cygwin paths

cygwin_volumes.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/cygwin.h>

struct dos_drive_mappings
{
  struct mapping
  {
    struct mapping *next;
    size_t doslen;
    size_t ntlen;
    wchar_t *dospath;
    wchar_t *ntdevpath;
  } *mappings;
};

void main (void)
{
  struct dos_drive_mappings *ddm = (struct dos_drive_mappings*)cygwin_internal(CW_ALLOC_DRIVE_MAP);

  for(struct mapping * p = ddm->mappings; p != NULL; p = p->next)
  {
    char * cygpath = cygwin_create_path(CCP_WIN_W_TO_POSIX, p->dospath);
    fwrite(cygpath, sizeof(char), strlen(cygpath) + 1, stdout);
    free(cygpath);
  }

  cygwin_internal(CW_FREE_DRIVE_MAP, ddm);
}