[llvm] Make WriteIndexesThinBackend multi threaded (PR #109847)

[Teresa Johnson via llvm-commits]

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@@ -1613,6 +1614,10 @@ namespace {
 class WriteIndexesThinBackend : public ThinBackendProc {
   std::string OldPrefix, NewPrefix, NativeObjectPrefix;
   raw_fd_ostream *LinkedObjectsFile;
+  DefaultThreadPool BackendThreadPool;
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teresajohnson wrote:

Can the common data members now be moved to the base class?

https://github.com/llvm/llvm-project/pull/109847