Generalize an IR verifier check to work with non-zero program address spaces

This commit modifies an existing IR verifier check that
assumes all functions will be located in the default address
space 0.

Rather than using the default paramater value getPointerTo(AddrSpace=0),
explicitly specify the program memory address space from the data layout.

This only affects targets that specify a nonzero address space
in their data layouts. The only in-tree target that does this
is AVR.

llvm-svn: 344243