Raise BuildFailed if cc command execution fails

This pull request causes tasks to raise an exception if `sh`ing the compiler commandline fails for some reason.
I'm planning to build `paper_house-config`, a simple `autoconf` replacement  (i.e. check for headers, functions etc. ), and would need this. It's obviously useful for other things too.

Ugh, about tests. I tried, but it's really hard to test these things with cucumber, which I also am not a big fan of.