RFR(S): JDK-8043780 Use open(O_CLOEXEC) instead of fcntl(FD_CLOEXEC)

[Martin Buchholz]

Hi,

I'd like to contribute a patch.

Webrev:
  http://cr.openjdk.java.net/~martin/webrevs/openjdk9/O_CLOEXEC/

Bug:
  https://bugs.openjdk.java.net/browse/JDK-8043780

If accepted, corresponding changes should be made to the other Unix
variants, but I can't do any testing there.