[Patch, libfortran] PR 40812 Large file support on MinGW

[Kai Tietz]

Interesting was that my last patch just worked as the restoration seek
use SEEK_CUR, which puzzled me a bit. Finally I found the real issue
here in the patch.
First I cleaned up this this temporary variable for comparison with
INVALID_HANDLE_VALUE. This define is a pointer already, and so no
scalar cast is necessary here.
Secondly for the seek to position to be truncated, FILE_CUR was used,
but of course it has to be seeked from beginning of file by
FILE_BEGIN.

This code I've tested for x86_64-pc-mingw32, i686-pc-mingw32. For w64
version and for mingw.org's version. The failed test Danny noticed,
works now well.

Cheers,
Kai

static int
raw_truncate (unix_stream * s, gfc_offset length)
{
#ifdef __MINGW32__
  LARGE_INTEGER tmp;
  HANDLE h;
  gfc_offset old;

  if (isatty (s->fd))
    {
      errno = EBADF;
      return -1;
    }
  old = lseek (s->fd, 0, SEEK_CUR);
  h = _get_osfhandle (s->fd);
  if (h == INVALID_HANDLE_VALUE)
    {
      runtime_error ("Couldn't get handle from fd");
      return -1;
    }
  tmp.QuadPart = length;
  if (!SetFilePointerEx (h, tmp, NULL, FILE_BEGIN))
    {
      runtime_error ("Couldn't seek to specified position for truncation");
      return -1;
    }
  if (!SetEndOfFile (h))
    {
      runtime_error ("Couldn't truncate file");
      return -1;
    }
  lseek (s->fd, old, SEEK_SET);
  return 0;
#elif defined HAVE_FTRUNCATE
  return ftruncate (s->fd, length);
#elif defined HAVE_CHSIZE
  return chsize (s->fd, length);
#else
  runtime_error ("required ftruncate or chsize support not present");
  return -1;
#endif
}

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