[DebugInfo] Sort the SDDbgValue list before assuming it is in IR order

Summary:
This code iterates the 'Orders' vector in parallel with the DbgValue
list, emitting all DBG_VALUEs that occurred between the last IR order
insertion point and the next insertion point. This assumes the
SDDbgValue list is sorted in IR order, which it usually is. However, it
is not sorted when a node with a debug value is replaced with another
one. When this happens, TransferDbgValues is called, and the new value
is added to the end of the list.

The problem can be solved by stably sorting the list by IR order.

Reviewers: aprantl, Ka-Ka

Reviewed By: aprantl

Subscribers: MatzeB, hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D38197

llvm-svn: 314114