Use correct C++11 header for std::swap()

Summary:
This is a backport of Core PR17634 [2/2]
https://github.com/bitcoin/bitcoin/pull/17634/commits/98fbd1cdffaa69357091cc67e959ac21119dfa16

Depends on D8281

The header algorithm is needed in cuckoocache.h for std::find (see PR18565). I'm not sure how Core got away with removing it for multiple months, for us it cause a compiler error.

Test Plan: ninja && ninja check

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D8282