Fix LLVM version check for ThinLTO import/export lists

These types changed in LLVM 18, not LLVM 17.

Author: nikic

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -1118,7 +1118,7 @@ struct LLVMRustThinLTOData {
 
   // Not 100% sure what these are, but they impact what's internalized and
   // what's inlined across modules, I believe.
-#if LLVM_VERSION_GE(17, 0)
+#if LLVM_VERSION_GE(18, 0)
   DenseMap<StringRef, FunctionImporter::ImportMapTy> ImportLists;
   DenseMap<StringRef, FunctionImporter::ExportSetTy> ExportLists;
   DenseMap<StringRef, GVSummaryMapTy> ModuleToDefinedGVSummaries;