Issues with clock_gettime(CLOCK_REALTIME, &wait) pre macOS 10.13

[Chris Jones]

Hi,

I've stumbled into the same issue twice in recent days, with two 
different ports, which is the use of

clock_gettime(CLOCK_REALTIME, &wait);

which is only available in macOS 10.12 or newer. See for instance the 
issue I found yesterday in xrootd.

https://github.com/xrootd/xrootd/issues/846

I am still waiting to see what upstream say, but I am hopeful they will 
consider it a bug. ( It would seem quite extreme to reduce the supported 
OSX releases from 10.7+ to 10.12+ in a minor patch revision...)

But I was wondering, is this something anyone else has stumbled over, 
and do we have a way of fixing this particular issue in the older OSes ?

Chris