Fix remaining -Wreturn-std-move violations in fbcode (#17308)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17308
In some cases there is still no RVO/NRVO and std::move is still needed. Latest
Clang gained -Wreturn-std-move warning to detect cases like this (see
https://reviews.llvm.org/D43322).
Reviewed By: igorsugak
Differential Revision: D14150915
fbshipit-source-id: 0df158f0b2874f1e16f45ba9cf91c56e9cb25066
