Make build.p6 more universal
Make build.p6 more universal

We've been using an almost identical script for MoarVM, it's time to
bring them back together.

In theory, now it should be easy to throw in some other backends.

Somehow I don't like the code here. Refactoring is welcome!

perl6/whateverable,MasterDuke17/whateverable,perl6/whateverable,perl6/whateverable