Move instances of std::function.

Or replace with llvm::function_ref if it's never stored. NFC intended.

llvm-svn: 272513
diff --git a/llvm/lib/Transforms/Utils/CloneModule.cpp b/llvm/lib/Transforms/Utils/CloneModule.cpp
index 6fb86da..4eed604 100644
--- a/llvm/lib/Transforms/Utils/CloneModule.cpp
+++ b/llvm/lib/Transforms/Utils/CloneModule.cpp
@@ -38,7 +38,7 @@
 
 std::unique_ptr<Module> llvm::CloneModule(
     const Module *M, ValueToValueMapTy &VMap,
-    std::function<bool(const GlobalValue *)> ShouldCloneDefinition) {
+    function_ref<bool(const GlobalValue *)> ShouldCloneDefinition) {
   // First off, we need to create the new module.
   std::unique_ptr<Module> New =
       llvm::make_unique<Module>(M->getModuleIdentifier(), M->getContext());