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/CodeGen/AtomicExpandPass.cpp b/llvm/lib/CodeGen/AtomicExpandPass.cpp
index 433ba94..4b26b64 100644
--- a/llvm/lib/CodeGen/AtomicExpandPass.cpp
+++ b/llvm/lib/CodeGen/AtomicExpandPass.cpp
@@ -59,7 +59,7 @@
     bool tryExpandAtomicRMW(AtomicRMWInst *AI);
     bool expandAtomicOpToLLSC(
         Instruction *I, Value *Addr, AtomicOrdering MemOpOrder,
-        std::function<Value *(IRBuilder<> &, Value *)> PerformOp);
+        function_ref<Value *(IRBuilder<> &, Value *)> PerformOp);
     AtomicCmpXchgInst *convertCmpXchgToIntegerType(AtomicCmpXchgInst *CI);
     bool expandAtomicCmpXchg(AtomicCmpXchgInst *CI);
     bool isIdempotentRMW(AtomicRMWInst *AI);
@@ -514,7 +514,7 @@
 
 bool AtomicExpand::expandAtomicOpToLLSC(
     Instruction *I, Value *Addr, AtomicOrdering MemOpOrder,
-    std::function<Value *(IRBuilder<> &, Value *)> PerformOp) {
+    function_ref<Value *(IRBuilder<> &, Value *)> PerformOp) {
   BasicBlock *BB = I->getParent();
   Function *F = BB->getParent();
   LLVMContext &Ctx = F->getContext();