Explicitly disable RelLookupTableConvertedPass

Before the passmanager update, the function `populateModulePassManager`
was called instead of `buildPerModuleDefaultPipeline` to set the default
passes. But the former did not have `RelLookupTableConverterPass` turned on
by default.

lib/Interpreter/BackendPasses.cpp

@@ -378,13 +378,19 @@ void BackendPasses::CreatePasses(int OptLevel, llvm::ModulePassManager& MPM,
           P.equals("ModuleInlinerPass") || P.equals("InlinerPass") ||
           P.equals("InlineAdvisorAnalysis") ||
           P.equals("PartiallyInlineLibCallsPass") ||
+          P.equals("RelLookupTableConverterPass") ||
           P.equals("InlineCostAnnotationPrinterPass") ||
           P.equals("InlineSizeEstimatorAnalysisPrinterPass") ||
           P.equals("InlineSizeEstimatorAnalysis"))
         return false;
 
       return true;
     });
+  } else {
+    // Register a callback for disabling RelLookupTableConverterPass.
+    PIC.registerShouldRunOptionalPassCallback([](StringRef P, Any) {
+      return !P.equals("RelLookupTableConverterPass");
+    });
   }
 
   SI.registerCallbacks(PIC, &FAM);