Fix TVM compile without LLVM

[trevor-m]

#7398 introduced an compilation error when using USE_LLVM=OFF. Fix by adding preprocessor if guard.

tvm/src/target/metadata_module.cc:120:23: error: ‘CreateLLVMCrtMetadataModule’ was not declared in this scope                                                   
       target_module = CreateLLVMCrtMetadataModule(crt_exportable_modules, target);