Fix two "msort()" vs "msortv()" issues in "arc land"
Fix two "msort()" vs "msortv()" issues in "arc land"

Summary: See <https://github.com/phacility/arcanist/pull/242>. Ref T13303. A little more fallout turned up in `arc`.

Test Plan: `grep msort(`

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13303

Differential Revision: https://secure.phabricator.com/D20605

phacility/arcanist,codelabs-ch/arcanist,codelabs-ch/arcanist,codelabs-ch/arcanist,phacility/arcanist,uber/arcanist,phacility/arcanist,Khan/arcanist,uber/arcanist,phacility/arcanist,codelabs-ch/arcanist,uber/arcanist,phacility/arcanist,uber/arcanist,codelabs-ch/arcanist,Khan/arcanist,Khan/arcanist,Khan/arcanist