[tz] zic.c's dolink() fails on some Windows filesystems

[Tom Lane via tz]

I have a report[1] that tzcode 2026b fails on Windows filesystems
that lack hard links, because it copes if link() fails with
ENOTSUP but what is actually returned is EINVAL.  I suggest
something along the lines of

            if (link(target, outname) == 0) {
              link_errno = 0;
              break;
            }
            link_errno = errno;
+           /* Windows returns EINVAL if filesystem lacks hard links. */
+           if (link_errno == EINVAL)
+             link_errno = ENOTSUP;
          }

paralleling the workaround for ancient Linux a few lines above.

                        regards, tom lane

[1] 
https://www.postgresql.org/message-id/e6122f9b2eef9096f1f11ecc058bcd91%40postgrespro.ru