Fix warnings

Summary:
Extra `;`, shadowed declarations and unitialised variables
were causing warnings to callers.

Reviewed By: stepancheg

Differential Revision: D19537831

fbshipit-source-id: 259cf9974592191c84d424bbdf3bd1c68425a76c

folly/detail/TurnSequencer.h

@@ -124,7 +124,7 @@ struct TurnSequencer {
     const uint32_t effectiveSpinCutoff =
         updateSpinCutoff || prevThresh == 0 ? kMaxSpinLimit : prevThresh;
 
-    uint64_t begin;
+    uint64_t begin = 0;
     uint32_t tries;
     const uint32_t sturn = turn << kTurnShift;
     for (tries = 0;; ++tries) {

folly/experimental/observer/detail/Core.h

@@ -52,8 +52,8 @@ class Core : public std::enable_shared_from_this<Core> {
   struct VersionedData {
     VersionedData() {}
 
-    VersionedData(std::shared_ptr<const void> data_, size_t version_)
-        : data(std::move(data_)), version(version_) {}
+    VersionedData(std::shared_ptr<const void> dat, size_t ver)
+        : data(std::move(dat)), version(ver) {}
 
     std::shared_ptr<const void> data;
     size_t version{0};