[inductor] make multi-kernel work with cpp-wrapper (#117813)
Make multi-kernel work with cpp-wrapper. multi-kernel generates two equivalent variants for a reduction. At runtime the faster one is picked. But cpp-wrapper need save cubin file during codegen. They don't work with each other at the beginning.
Thanks Jason for suggesting a neat way to integrate these two. cpp-wrapper does 2 passes codegen right now. For the first pass, we still generate multi-kernel code and run it; for the second pass, we load the cubin file for the faster kernel directly. And multi-kernel python code is not generated for the second pass since they should not be needed.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/117813
Approved by: https://github.com/jansel
