[libc][NFC] Rename cpp::function to cpp::Function.

Summary: Just to be consistent with other names in cpp.

Reviewers: abrachet

Subscribers: tschuett, libc-commits

Tags: #libc-project

Differential Revision: https://reviews.llvm.org/D79189

GitOrigin-RevId: 675eea46f0452933170bb94307867dca8d9c80b9
2 files changed