Repeatedly divide read buffer size by 8 until success. Fixes #11481.

Dividing by 8 leads to success on the second try in the case of the failure of --lisp on Windows 7.

src/support/ios.c

@@ -99,14 +99,19 @@ static int _os_read(long fd, void *buf, size_t n, size_t *nread)
 {
  ssize_t r;
 
+ unsigned int sz = LIMIT_IO_SIZE(n);
  while (1) {
  set_io_wait_begin(1);
- r = read((int)fd, buf, LIMIT_IO_SIZE(n));
+ r = read((int)fd, buf, sz);
  set_io_wait_begin(0);
  if (r > -1) {
  *nread = (size_t)r;
  return 0;
  }
+ if (errno == ENOMEM && sz > 80) {
+ sz >>= 3;
+ continue;
+ }
  if (!_enonfatal(errno)) {
  *nread = 0;
  return errno;