Fix XNNPACK missing symbol from post-operation.c (#94768)
Summary: Fix RL team XNNPACK xnn_mutex.h issue.
Test Plan: buck2 test
Reviewed By: kirklandsign
Differential Revision: D43243129
Pull Request resolved: https://github.com/pytorch/pytorch/pull/94768
Approved by: https://github.com/kirklandsign, https://github.com/digantdesai
