[libc] Add spec for sigdelset and sigfillset.

Summary: Caught by libc-tidy from patch D77281.

Reviewers: abrachet, sivachandra

Reviewed By: abrachet

Subscribers: mgorny, tschuett, libc-commits

Tags: #libc-project

Differential Revision: https://reviews.llvm.org/D78703

GitOrigin-RevId: 29213878e7dc0c329b57c60aac87a3cf392416fc
3 files changed