Add syscalls for process times

[dimakuv]

Below APIs are used by the openSSL speed test:

clock_t now = times(&rus);
sysconf(_SC_CLK_TCK);
getrusage(RUSAGE_SELF, &rus);

See https://github.com/openssl/openssl/blob/6514dee7264d30be1ab9ab07f9798071184e7b7a/apps/lib/apps.c#L2246

We need to implement these APIs/syscalls in Graphene.