Fix build under MSVC 2015 Update 3

Summary: MSVC 2015 Update 3 can't parse these with curly-brace init'd, so swap the assignment. The result is the exact same.

Reviewed By: simpkins

Differential Revision: D7508756

fbshipit-source-id: 5e60607f978a87ae8bfed22086d1dccef15759ac

folly/synchronization/Rcu-inl.h

@@ -21,7 +21,7 @@
 namespace folly {
 
 template <typename Tag>
-bool rcu_domain<Tag>::singleton_{false};
+bool rcu_domain<Tag>::singleton_ = false;
 
 template <typename Tag>
 rcu_domain<Tag>::rcu_domain(Executor* executor) noexcept

folly/synchronization/detail/ThreadCachedInts.h

@@ -171,7 +171,7 @@ class ThreadCachedInts {
 
 template <typename Tag>
 thread_local typename detail::ThreadCachedInts<Tag>::Integer*
-    detail::ThreadCachedInts<Tag>::int_cache_{nullptr};
+    detail::ThreadCachedInts<Tag>::int_cache_ = nullptr;
 
 } // namespace detail
 } // namespace folly