8011536: (fs) BasicFileAttributes.creationTime() should return birth time (mac)

[Alan Bateman]

One of the things left over from the Mac port is to return the 
st_birthtime as the creationFile attribute. This can be exposed in the 
stat structure on 64-bit builds. As part of this, I've cleaned-up the 
handling of optional sys calls as we were missing a way to indicate if 
futimes (or futimesat) is supported or not.

The webrev with the proposed changes is here:

http://cr.openjdk.java.net/~alanb/8011536/webrev/

-Alan.