OS X build

[miroslavolek]

I noticed that current branch has no support for OSX build, I think it's shame cause it works fine on OSX with Maya 2018.

[miroslavolek]

For anyone who has problem with compiling CodeTimings.cpp, this patch should fix it:

https://gist.github.com/miroslavolek/76ef9f4e5d5386f55a231e494cdf40de

[robthebloke]

you might as well just submit a PR with the fix (and any other macosx cmake changes, et al) - probably the fastest way to get it into the build. Only minor issue, is that we have no way to test a mac build internally at this time (so errors in the mac build may slip in every so often)