PassWrapper: adapt for llvm/llvm-project@b01e2a8

A boolean turned into an enum. None matches the old behavior of false,
so we pass that.

@rustbot label: +llvm-main

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -827,9 +827,14 @@ extern "C" LLVMRustResult LLVMRustOptimize(
       !NoPrepopulatePasses) {
     PipelineStartEPCallbacks.push_back(
         [](ModulePassManager &MPM, OptimizationLevel Level) {
-          MPM.addPass(LowerTypeTestsPass(/*ExportSummary=*/nullptr,
-                                         /*ImportSummary=*/nullptr,
-                                         /*DropTypeTests=*/false));
+          MPM.addPass(LowerTypeTestsPass(
+              /*ExportSummary=*/nullptr,
+              /*ImportSummary=*/nullptr,
+#if LLVM_VERSION_GE(20, 0)
+              /*DropTypeTests=*/llvm::lowertypetests::DropTestKind::None));
+#else
+              /*DropTypeTests=*/false));
+#endif
         });
   }