[llvm] [CodeGen] Let `PassBuilder` support machine passes (PR #76320)

[via llvm-commits]

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@@ -461,8 +461,7 @@ class LLVMTargetMachine : public TargetMachine {
   }
 
   virtual std::pair<StringRef, bool> getPassNameFromLegacyName(StringRef) {
-    llvm_unreachable(
-        "getPassNameFromLegacyName parseMIRPipeline is not overridden");
+    llvm_unreachable("getPassNameFromLegacyName is not overridden");
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paperchalice wrote:

This method is still necessary during migration, for `start/stop-before/after=<...>`, although `PassBuilder` is a better place to implement it.

https://github.com/llvm/llvm-project/pull/76320