[llvm] [CodeGen] Support start/stop in CodeGenPassBuilder (PR #70912)

[Arthur Eubanks via llvm-commits]

================
@@ -469,20 +486,36 @@ template <typename DerivedT> class CodeGenPassBuilder {
   const DerivedT &derived() const {
     return static_cast<const DerivedT &>(*this);
   }
+
+  void setStartStopPasses(const TargetPassConfig::StartStopInfo &Info) const;
+
+  Error verifyStartStop(const TargetPassConfig::StartStopInfo &Info) const;
+
+  mutable SmallVector<llvm::unique_function<bool(StringRef)>, 4>
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aeubanks wrote:

it seems nicer to keep this in `AddPass`. is the reason that these are moved out of `AddPass` because it references `Started`/`Stopped` in `CodeGenPassBuilder`? and there's no way to easily validate them if these are somewhere else?

https://github.com/llvm/llvm-project/pull/70912