[clang] [clang-tools-extra] [libc] [libc][c11] implement ctime (PR #107285)

[Зишан Мирза via cfe-commits]

zimirza wrote:

Thank you for the thorough review. I really do appreciate it. I have a question. Since this pull request is a new API feature implementation, should I also update documentation for `ctime` and `ctime_r`?

https://github.com/llvm/llvm-project/pull/107285