Mach status support

[Sergey]

When I worked with one C code translation, I found that command 
clock_gettime, that available in POSIX systems is not implemented 
in MacOS.
This SO thread

https://stackoverflow.com/questions/5167269/clock-gettime-alternative-in-mac-os-x

suggested some workaround implementations, which using some mach 
headers like mach.h and mach_time.h

But when I’ve checked dmd sources

https://github.com/dlang/dmd/tree/master/druntime/src/core/sys/darwin/mach

I didn’t find it. So currently I’ve used MonoTime as temporary 
solution (however I’m not sure if it is a proper alternative).

How full is dmd specific implementation of Darwin and Mach 
headers?
Any plans to improve it (in case it is not full right now)?