Add corner case logic to BasicStoreManager and GRSimpleVals::EvalBinOp to enable

Add corner case logic to BasicStoreManager and GRSimpleVals::EvalBinOp to enable
reasoning about OSCompareAndSwap32Barrier/OSCompareAndSwap64Barrier. Essentially
the address of reference to a region (pointer-to-pointer) can be casted to
(int32_t*), and we need to handle the logic to convert the involved locations
back and forth from nonloc::LocAsInteger, nonloc::ConcreteInt, to Loc and
loc::ConcreteInt respectively. This adds some potentially suspect logic to
BasicStoreManager that allows the analyzer to reason about abuses of the C type
system. This should probably be refined, be ported over to RegionStoreManager,
and extended with "path-sensitive type checking" to flag bugs in clearly
incoherent code.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@70382 91177308-0d34-0410-b5e6-96231b3b80d8