[Unittests] Fix a build failure with clang 3.8. NFCI.

llvm-svn: 297423
diff --git a/llvm/unittests/ADT/STLExtrasTest.cpp b/llvm/unittests/ADT/STLExtrasTest.cpp
index f17d24f..6c162de 100644
--- a/llvm/unittests/ADT/STLExtrasTest.cpp
+++ b/llvm/unittests/ADT/STLExtrasTest.cpp
@@ -69,7 +69,7 @@
 
   // Test an empty range.
   IntResults.clear();
-  const std::vector<int> baz;
+  const std::vector<int> baz{};
   for (auto X : llvm::enumerate(baz)) {
     IntResults.emplace_back(X.Index, X.Value);
   }