[DebugInfo] Fix multi-byte entry values in call site values

Summary:
In D67768/D67492 I added support for entry values having blocks larger
than one byte, but I now noticed that the DIE implementation I added there
was broken. The takeNodes() function, that moves the entry value block
from a temporary buffer to the output buffer, would destroy the input
iterator when transferring the first node, meaning that only that node
was moved.

In practice, this meant that when emitting a call site value using a
DW_OP_entry_value operation with a DWARF register number larger than 31,
that multi-byte DW_OP_regx expression would be truncated.

Reviewers: djtodoro, aprantl, vsk

Reviewed By: djtodoro

Subscribers: llvm-commits

Tags: #debug-info, #llvm

Differential Revision: https://reviews.llvm.org/D76279