[OffloadPackager] Add necessary move statement on returned value

Summary:
Some older compilers cannot automatically elide the returned vector of
unique pointers, causing build errors. This patch explicitly moves the
returned value instead which should solve the problem.

clang/tools/clang-offload-packager/ClangOffloadPackager.cpp

@@ -143,7 +143,7 @@ extractOffloadFiles(MemoryBufferRef Contents) {
     Binaries.emplace_back(std::move(*BinaryOrErr));
   }
 
-  return Binaries;
+  return std::move(Binaries);
 }
 
 static Error unbundleImages() {