Update pthreadpool (#55950)
Summary:
This updates pthreadpool to include [this commit](https://github.com/Maratyszcza/pthreadpool/commit/a134dd5d4cee80cce15db81a72e7f929d71dd413), which removes a bunch of deprecation warnings in the build.
Fixes https://github.com/pytorch/pytorch/issues/33760
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55950
Reviewed By: mruberry
Differential Revision: D27773417
Pulled By: driazati
fbshipit-source-id: b4397787d882228bae47ddd8ccf628047466b904
