Revert "Remove redundant "std::move"s in return statements"

The build failed with

  error: call to deleted constructor of 'llvm::Error'

errors.

This reverts commit 1c2241a7936bf85aa68aef94bd40c3ba77d8ddf2.
diff --git a/llvm/tools/llvm-jitlink/llvm-jitlink.cpp b/llvm/tools/llvm-jitlink/llvm-jitlink.cpp
index df04a2e..26bcf46 100644
--- a/llvm/tools/llvm-jitlink/llvm-jitlink.cpp
+++ b/llvm/tools/llvm-jitlink/llvm-jitlink.cpp
@@ -238,8 +238,8 @@
     std::unique_ptr<JITLinkSlabAllocator> Allocator(
         new JITLinkSlabAllocator(SlabSize, Err));
     if (Err)
-      return Err;
-    return Allocator;
+      return std::move(Err);
+    return std::move(Allocator);
   }
 
   Expected<std::unique_ptr<JITLinkMemoryManager::Allocation>>