[libc] [llvm] [libc][c11] Add stdio.h's rename() function (PR #85068)

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

So the availability of `SYS_rename` or `SYS_renameat` seems like they might not exist (have been removed for newer architectures) while `SYS_renameat2` might not exist (for ancient kernels, though I guess that's true for all syscalls).

Because we don't need to support such prehistoric kernels, I suspect this is a syscall that we'll need to implement in terms of SYS_renameat2.

https://github.com/llvm/llvm-project/pull/85068