Fix build failure with GCC 5

Summary:
GCC 5 doesn't recognize LOG(FATAL) as [[noreturn]],
so remove [[noreturn]] to avoid that warning and build failure.

Reviewed By: yfeldblum

Differential Revision: D4484625

fbshipit-source-id: ca129ca3a52239becd7d80f99107e64745bf8838

folly/detail/ThreadLocalDetail.h

@@ -257,7 +257,7 @@ struct StaticMetaBase {
   StaticMetaBase(ThreadEntry* (*threadEntry)(), bool strict);
 
   [[noreturn]] ~StaticMetaBase() {
-    LOG(FATAL) << "StaticMeta lives forever!";
+    folly::assume_unreachable();
   }
 
   void push_back(ThreadEntry* t) {