folly/test/ThreadLocalTest.cpp: avoid shadowing warnings

Summary: Fix warnings exposed by the upstream-proposed -Wshadow-compatible-local option.

Reviewed By: andrewjcg

Differential Revision: D4041950

fbshipit-source-id: 7c18564273c5839c647709307f56b2fb5e0f6588

folly/test/ThreadLocalTest.cpp

@@ -425,7 +425,7 @@ TEST(ThreadLocal, Stress) {
   std::vector<std::thread> threads;
   threads.reserve(numThreads);
 
-  for (size_t i = 0; i < numThreads; ++i) {
+  for (size_t k = 0; k < numThreads; ++k) {
     threads.emplace_back([&objects] {
       for (size_t rep = 0; rep < numReps; ++rep) {
         for (size_t i = 0; i < objects.size(); ++i) {