[xnnpack][Bug Fix] Pass serialized model by reference (#89089)
Two changes
- Remove XNNCompiler Dependence on std::string by passing void*
- Grab ser_model by reference: This bug was causing data pointers given to xnn_runtime to be freed because ser_model was on the stack.
Differential Revision: [D41208380](https://our.internmc.facebook.com/intern/diff/D41208380/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/89089
Approved by: https://github.com/digantdesai
