[libc] comparing with glibc for ctime, llvm implementation has an offset by 1 hour

[zimirza]

In main branch, not released version:

For t=0, glibc's ctime returns Thu Jan 1 01:00:00 1970\n, while llvm's ctime returns Thu Jan 1 00:00:00 1970\n.

For t=2147483647, glibc's ctime returns Tue Jan 19 04:14:07 2038\n, while llvm's ctime returns Tue Jan 19 03:14:07 2038\n.

It might be better to be consistent with glibc's implementation for compatibility reasons.