Pass the llvm IR pointer value and offset to the constructor of

MachinePointerInfo when getStore is called to create a node that stores an
argument passed in register to the stack. Without this change, the post RA 
scheduler will fail to discover the dependencies between the stores
instructions and the instructions that load from a structure passed by value. 

The link to the related discussion is here:
http://lists.cs.uiuc.edu/pipermail/llvmdev/2012-March/048055.html

llvm-svn: 153499