Fix class member shadowing in folly::ProducerConsumerQueue

Summary: Previous version failed to compile with "-Werror=shadow" flag, this commit fixes the problem.

Reviewed By: WillerZ

Differential Revision: D5255814

fbshipit-source-id: c1252474ed5415b47759022bcbabc78c1639e10a

folly/ProducerConsumerQueue.h

@@ -64,12 +64,12 @@ struct ProducerConsumerQueue {
     // (No real synchronization needed at destructor time: only one
     // thread can be doing this.)
     if (!std::is_trivially_destructible<T>::value) {
-      size_t read = readIndex_;
-      size_t end = writeIndex_;
-      while (read != end) {
-        records_[read].~T();
-        if (++read == size_) {
-          read = 0;
+      size_t readIndex = readIndex_;
+      size_t endIndex = writeIndex_;
+      while (readIndex != endIndex) {
+        records_[readIndex].~T();
+        if (++readIndex == size_) {
+          readIndex = 0;
         }
       }
     }