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

folly/detail/ThreadLocalDetail.cpp

@@ -17,6 +17,7 @@
 
 namespace folly { namespace threadlocal_detail {
 
+MAX_STATIC_CONSTRUCTOR_PRIORITY
 PthreadKeyUnregister PthreadKeyUnregister::instance_;
 
 }}