Add MAX_STATIC_CONSTRUCTOR_PRIORITY to PthreadKeyUnregister
Add MAX_STATIC_CONSTRUCTOR_PRIORITY to PthreadKeyUnregister

Summary: We want onThreadExit to be canceled as late as possible. Otherwise accessAllThreads() may crash on shutdown (because ThreadEntry is destroyed, but not removed from the global list).

Reviewed By: igorsugak

Differential Revision: D2923435

fb-gh-sync-id: 3a8eef05844bb547c06db33cb96734df1169852a
shipit-source-id: 3a8eef05844bb547c06db33cb96734df1169852a

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