Fixing pthreadpool symbol conflict issue. (#33869)
Summary:
Mainly renaming pthread_create of C2, the only one referred internally in NNPACK, that
is conflicting, to pthread_create_c2.
Removed 2 other conflicting symbols that are not used internally at all.
Pointing XNNPACK to original repo instead of the fork.
Copy pasted the new interface and implementation to
caff2/utils/threadpool, so that for internal builds we compile against
this.
When threadpool is unified this will be removed.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33869
Differential Revision: D20140580
Pulled By: kimishpatel
fbshipit-source-id: de70df0af9c7d6bc065e85ede0e1c4dd6a9e6be3
