[llvm] [DWARFLinker][DWARFLinkerParallel][NFC] Refactor DWARFLinker&DWARFLinkerParallel to have a common library. Part 1. (PR #75925)

[Alexander Yermolovich via llvm-commits]

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@@ -9,8 +9,9 @@
 #include "DependencyTracker.h"
 #include "llvm/Support/FormatVariadic.h"
 
-namespace llvm {
-namespace dwarflinker_parallel {
+using namespace llvm;
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ayermolo wrote:

why switch to using here? 

https://github.com/llvm/llvm-project/pull/75925