Don't double-link object files built from generated C.
Merge pull request #221 from yallop/duplicate-objects

Don't double-link object files built from generated C.
attempt to add bool type corresponding to the llvm i1

The idea is to find a way to represet the llvm i1 type, since llvm
ExecutionEngine also uses libffi now. It's a single bit, but I thought
I'd try to coerce it from an i8 (char). This proof-of-concept requires
more work, especially in the area of tests.