More helpful error-message than "The exception was: ExitFailure 1"

Hi!

This is a proposal to make life little easier for beginners. I don't know how much work this would require, wanted to discuss possible solutions before looking into.

Currently, it's very common to see error like this when compilation fails:

```
somepackage-4.0 failed during the building phase. The exception was:
ExitFailure 1
```

I just figured out that I was so used to it that almost thought of it as a "normal thing". But it isn't, and I'd like to discuss possible enhancements to this, especially from people who are familiar with cabal's code-base.