hunkgen: satisfy the clang 22 ComplierInstance VFS invariant.

ThunkLibs/Generator/gen.cpp

@@ -812,6 +812,9 @@ bool GenerateThunkLibsActionFactory::runInvocation(std::shared_ptr<clang::Compil
 #else
   clang::CompilerInstance Compiler(std::move(PCHContainerOps));
   Compiler.setInvocation(std::move(Invocation));
+#endif
+#if LLVM_VERSION_MAJOR >= 22
+  Compiler.setVirtualFileSystem(Files->getVirtualFileSystemPtr());
 #endif
   Compiler.setFileManager(Files);