[swift-evolution] Print stack trace for fatalError

[Chris Lattner]

> On Dec 7, 2015, at 1:24 PM, Radoslaw Pietruszewski via swift-evolution <swift-evolution at swift.org> wrote:
> 
> + 1. This should also be generalized to assert, precondition, etc. If there was a way for custom fatalError-like functions to also dump a stack trace, that would be great.

Improvements to this area would be great. :-)

-Chris