Make the LLParser accept call instructions of variables in the program AS

Summary:
Since r325479 the DataLayout includes a program address space. However, it
is not possible to use `call %foo` if foo is a `i8(...) addrspace(200)` and
the DataLayout specifies address space 200 as the address space for functions.
With this change the IR parser will still accept variables in the program
address space as well as address space 0 for call and invoke functions.

Reviewers: pcc, arsenm, bjope, dylanmckay, theraven

Reviewed By: dylanmckay

Subscribers: wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D43645

llvm-svn: 326188