Allow the import of multi-dimensional access functions

Originally, we disallowed the import of multi-dimensional access functions due
to our code generation not supporting the generation of new address expressions
for multi-dimensional memory accesses. When building our run-time alias check
infrastructure we added code generation support for multi-dimensional address
calculations.  Hence, we can now savely allow the import of new
multi-dimensional access functions.

llvm-svn: 246917