DebugInfo: Remove special iterators from DIExpression

Remove special iterators from `DIExpression` in favour of same in
`MDExpression`.  There should be no functionality change here.

Note that the APIs are slightly different: `getArg(unsigned)` counts
from 0, not 1, in the `MDExpression` version of the iterator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234285 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -1511,7 +1511,8 @@ static void emitDebugLocValue(const AsmPrinter &AP,
       // Complex address entry.
       if (Loc.getOffset()) {
         DwarfExpr.AddMachineRegIndirect(Loc.getReg(), Loc.getOffset());
-        DwarfExpr.AddExpression(Expr.begin(), Expr.end(), PieceOffsetInBits);
+        DwarfExpr.AddExpression(Expr->expr_op_begin(), Expr->expr_op_end(),
+                                PieceOffsetInBits);
       } else
         DwarfExpr.AddMachineRegExpression(Expr, Loc.getReg(),
                                           PieceOffsetInBits);