[analyzer] Treat pointers to static member functions as function pointers

Sema treats pointers to static member functions as having function pointer
type, so treat treat them as function pointer values in the analyzer as well.
This prevents an assertion failure in SValBuilder::evalBinOp caused by code
that expects function pointers to be Locs (in contrast, PointerToMember values
are nonlocs).

Differential Revision: https://reviews.llvm.org/D28033

llvm-svn: 291581