[llvm] [CodeGen] Expose the extensibility of PassConfig to plugins (PR #139059)

[Stefan Gränitz via llvm-commits]

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@@ -119,6 +125,9 @@ class TargetMachine {
   std::optional<PGOOptions> PGOOption;
 
 public:
+  static ManagedStatic<SmallVector<PassConfigCallback, 1>>
+      TargetPassConfigCallbacks;
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weliveindetail wrote:

Could this be a non-static private member of `CodeGenTargetMachineImpl` instead? The `registerTargetPassConfigCallback()` would be virtual then like a few others already.

https://github.com/llvm/llvm-project/pull/139059