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

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

Looking into the riscv failure.
1. our `libc/config/linux/syscall_numbers.h.inc` `#include`'s `asm/unistd.h`.
2. on the riscv64 build bot, this is `/usr/include/riscv64-linux-gnu/asm/unistd.h` which just `#include`'s `/usr/include/asm-generic/unistd.h`.
3. `/usr/include/asm-generic/unistd.h` does not define `__NR_rename`.

It does have definitions for:
- `__NR_renameat`
- `__NR_renameat2`

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