Fix PR16110: Handle DBG_VALUE in ConnectedVNInfoEqClasses::Distribute().

Now that the LiveDebugVariables pass is running *after* register
coalescing, the ConnectedVNInfoEqClasses class needs to deal with
DBG_VALUE instructions.

This only comes up when rematerialization during coalescing causes the
remaining live range of a virtual register to separate into two
connected components.

llvm-svn: 182592