apple-gate ThreadLocal in fibers code

Summary: Some internal malloc shims broke on using folly::ThreadLocal, so only do that for `__APPLE__`.

Reviewed By: @brianwatling

Differential Revision: D2151318

folly/experimental/fibers/FiberManager-inl.h

@@ -22,7 +22,9 @@
 #include <folly/Optional.h>
 #include <folly/Portability.h>
 #include <folly/ScopeGuard.h>
+#ifdef __APPLE__
 #include <folly/ThreadLocal.h>
+#endif
 #include <folly/experimental/fibers/Baton.h>
 #include <folly/experimental/fibers/Fiber.h>
 #include <folly/experimental/fibers/LoopController.h>
@@ -455,8 +457,13 @@ T& FiberManager::local() {
 
 template <typename T>
 T& FiberManager::localThread() {
+#ifndef __APPLE__
+  static thread_local T t;
+  return t;
+#else // osx doesn't support thread_local
   static ThreadLocal<T> t;
   return *t;
+#endif
 }
 
 inline void FiberManager::initLocalData(Fiber& fiber) {