Most users won't have to worry about this as all of the
'getOrInsertFunction' functions on Module will default to the program
An overload has been added to Function::Create to abstract away the
details for most callers.
This is based on https://reviews.llvm.org/D37054 but without the changes to
make passing a Module to Function::Create() mandatory. I have also added
some more tests and fixed the LLParser to accept call instructions for
types in the program address space.