Running unittests with optimizations enabled

[Guillaume Piolat]

Hello,

Here is a copy-and-paste tutorial about running unittests with 
optimizations.

https://p0nce.github.io/d-idioms/#Unittests-with-optimizations-:-the-Final-Frontier

This has a number of benefits, in particular this expose DMD 
codegen bugs more readily. Because organizations may depend on 
LLVM backend for production, which has more stable codegen, 
traditionally it can be a bit fruitless to test DMD releases with 
optimizations on. Hence, DMD codegen bugs gets _avoided_ instead 
of reported.

Your existing test suite may well be useful to find more DMD 
codegen bugs and frontend ICE.