Revert "DIBuilder: Remove dead code"

This reverts commit r218820.  It turns out that Adrian has an
outstanding SROA patch that uses this.

I've updated it to forward to `createExpression()`.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218828 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/DIBuilder.h

@@ -505,6 +505,14 @@ namespace llvm {
     /// @param Addr        An array of complex address operations.
     DIExpression createExpression(ArrayRef<int64_t> Addr = None);
 
+    /// createPieceExpression - Create a descriptor to describe one part
+    /// of aggregate variable that is fragmented across multiple Values.
+    ///
+    /// @param OffsetInBytes Offset of the piece in bytes.
+    /// @param SizeInBytes   Size of the piece in bytes.
+    DIExpression createPieceExpression(unsigned OffsetInBytes,
+                                       unsigned SizeInBytes);
+
     /// createFunction - Create a new descriptor for the specified subprogram.
     /// See comments in DISubprogram for descriptions of these fields.
     /// @param Scope         Function scope.