gcc-4.8 is not decaying types correctly in lambda init captures. Help it out....

gcc-4.8 is not decaying types correctly in lambda init captures. Help it out. Fixes open source build.

Summary: Trivial change gets folly::ThreadLocal building again with gcc-4.8, needed by the Open Source build.

Reviewed By: chadparry, yfeldblum

Differential Revision: D3498657

fbshipit-source-id: cf36f2bef7f1d03d133d16bfd063f7a2ce681822

folly/detail/ThreadLocalDetail.h

@@ -107,10 +107,11 @@ struct ElementWrapper {
     DCHECK(deleter2 == nullptr);
     if (p) {
       ptr = p;
-      deleter2 = new std::function<DeleterFunType>([d = d](
-          void* pt, TLPDestructionMode mode) {
-        d(static_cast<Ptr>(pt), mode);
-      });
+      auto d2 = d; // gcc-4.8 doesn't decay types correctly in lambda captures
+      deleter2 = new std::function<DeleterFunType>(
+          [d2](void* pt, TLPDestructionMode mode) {
+            d2(static_cast<Ptr>(pt), mode);
+          });
       ownsDeleter = true;
       guard.dismiss();
     }