remove unnecessary copies from FileUtils

Summary:
RVO only works when the local and the return type are exact
matches. Here, we're invoking the constructor, so we need to
std::move.

Reviewed By: xavierd

Differential Revision: D41097721

fbshipit-source-id: 52e4425a960ce0aa8ae59a827ddde4e9b58a7f92

Author: chadaustin

eden/fs/utils/FileUtils.cpp

@@ -24,7 +24,7 @@ folly::Try<std::string> readFile(AbsolutePathPiece path, size_t num_bytes) {
         fmt::format(FMT_STRING("couldn't read {}"), path))};
   }
 
-  return folly::Try{ret};
+  return folly::Try{std::move(ret)};
 }
 
 folly::Try<void> writeFile(AbsolutePathPiece path, folly::ByteRange data) {
@@ -66,7 +66,7 @@ folly::Try<std::vector<PathComponent>> getAllDirectoryEntryNames(
   for (const auto& entry : iter) {
     direntNames.emplace_back(entry.path().filename().c_str());
   }
-  return folly::Try{direntNames};
+  return folly::Try{std::move(direntNames)};
 }
 
 #else
@@ -178,7 +178,7 @@ folly::Try<std::string> readFile(AbsolutePathPiece path, size_t num_bytes) {
         GetLastError(), fmt::format(FMT_STRING("couldn't read {}"), path))};
   }
 
-  return folly::Try{ret};
+  return folly::Try{std::move(ret)};
 }
 
 folly::Try<void> writeFile(AbsolutePathPiece path, folly::ByteRange data) {