Fix build error on gcc.

llvm-svn: 304595
diff --git a/llvm/lib/ObjectYAML/CodeViewYAMLDebugSections.cpp b/llvm/lib/ObjectYAML/CodeViewYAMLDebugSections.cpp
index a85dcf9..21d2983 100644
--- a/llvm/lib/ObjectYAML/CodeViewYAMLDebugSections.cpp
+++ b/llvm/lib/ObjectYAML/CodeViewYAMLDebugSections.cpp
@@ -397,7 +397,7 @@
     DebugStringTableSubsection &Strings) {
   std::vector<std::unique_ptr<DebugSubsection>> Result;
   if (Subsections.empty())
-    return Result;
+    return std::move(Result);
 
   auto Checksums = findChecksums(Subsections);
   if (!Checksums)