[D-runtime] tzset and Mac OS X

[Jonathan M Davis]

Is there a reason why core.stdc.time does not have tzset() for OSX? It 
specifically has it for Linux and FreeBSD but not OSX. According to this man page 
( http://is.gd/hSSaf ), it exists on Mac OS X.

Either it needs to be made available in druntime, or I'm going to have to make 
the code that uses it in the new std.datetime unavailable for the Mac. It 
wouldn't be the end of the world, since the amount of code is fairly small, but 
if it's available on the Mac, then it seems to me that it should be available 
for the Mac in druntime, just like it is on Linux and FreeBSD.

- Jonathan M Davis