[llvm] [NFC][RABasic] Use `std::move` to avoid copy (PR #157825)

[Alexis Engelke via llvm-commits]

aengelke wrote:

Can't we make RegAllocFilterFunc a raw function pointer instead? I think none of the users require captures and std::function is inefficient.

https://github.com/llvm/llvm-project/pull/157825