[SDAG] Use index type size for offset accumulation

This is a precondition of the API. Not testable with in-tree
targets.

Fixes #134008.

Author: nikic

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -1564,7 +1564,7 @@ static bool processDbgDeclare(FunctionLoweringInfo &FuncInfo,
 
   // Look through casts and constant offset GEPs. These mostly come from
   // inalloca.
-  APInt Offset(DL.getTypeSizeInBits(Address->getType()), 0);
+  APInt Offset(DL.getIndexTypeSizeInBits(Address->getType()), 0);
   Address = Address->stripAndAccumulateInBoundsConstantOffsets(DL, Offset);
 
   // Check if the variable is a static alloca or a byval or inalloca