folly/test/SingletonTest.cpp: avoid shadowing warnings

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

Reviewed By: elsteveogrande

Differential Revision: D4041798

fbshipit-source-id: 9fb6901e791176eb42c31f287655aea6be95a30b

folly/test/SingletonTest.cpp

@@ -171,13 +171,11 @@ TEST(Singleton, NaughtyUsage) {
   SingletonNaughtyUsage2<Watchdog> watchdog_singleton;
 
   // double registration
-  EXPECT_DEATH([]() { SingletonNaughtyUsage2<Watchdog> watchdog_singleton; }(),
-               "");
+  EXPECT_DEATH([]() { SingletonNaughtyUsage2<Watchdog> w2; }(), "");
   vault2.destroyInstances();
 
   // double registration after destroy
-  EXPECT_DEATH([]() { SingletonNaughtyUsage2<Watchdog> watchdog_singleton; }(),
-               "");
+  EXPECT_DEATH([]() { SingletonNaughtyUsage2<Watchdog> w3; }(), "");
 }
 
 struct SharedPtrUsageTag {};