1. When a pointer to struct is used as an argument, GRSimpleVals::EvalCall()

   sets the whole struct to Unknown. Then we cannot assume the V passed to
   BindStruct() is always a CompoundVal. When it is an UnknownVal, we call
   BindStructToVal(UnknownVal).

2. Change the signature of InitializeStructToUndefined() to BindStructToVal()
   to reuse the code.

llvm-svn: 58564