[libc] Add strlen implementation.

Summary: This should fix the call to a non internal libc function.

Reviewers: sivachandra, abrachet

Reviewed By: sivachandra

Subscribers: xbolva00, mgorny, MaskRay, tschuett, libc-commits

Tags: #libc-project

Differential Revision: https://reviews.llvm.org/D77279

GitOrigin-RevId: 1fcfd30fae76fb1d30906a65c670cce32fd5cf15
8 files changed