[phobos] Showstopper bug: Hello world fails on OSX!

[Don Clugston]

Bug 4854. "Regression(2.047, Mac only) writefln Segmentation fault if
no globals"  Confirmed by 3 people.

Thread local storage isn't getting set up correctly. Perhaps this
happens when TLS is used in a library, but not in user code.
This behaviour was introduced in 2.047, though it may have been a
latent bug which was only triggered in that release.
This may be a druntime bug, though it is more likely to be a compiler bug.

Although this is OSX-specific, this bug could still be a PR disaster.
Perhaps an OSX user can track down which svn commit triggered the regression.