Fix torch.compile g++ flag error on ppc64le (#104956)
g++ flag -march is not recognised on ppc64le. So adding a check for platform machine to be ppc64le and using -mcpu flag instead. Other architectures will still use -march flag
This fixes the torch.compile feature failure on ppc64le
Pull Request resolved: https://github.com/pytorch/pytorch/pull/104956
Approved by: https://github.com/jgong5, https://github.com/jansel
