Amend the recent update to VG_(getrlimit) and VG_(setrlimit)

Amend the recent update to VG_(getrlimit) and VG_(setrlimit)

[get|set]rlimit system calls are becoming deprecated.
Coregrind should use prlimit64 as the first candidate in order to
achieve "rlimit" functionality.

There are also systems that do not even support older "rlimits".

Modify the previously added support VG_(getrlimit) and VG_(setrlimit)
using __NR_prlimit64 by making it similar to the glibc implementation.

It fixes none/tests/stackgrowth and none/tests/sigstackgrowth
tests on nanoMIPS.

Patch by: Stefan Maksimovic and Aleksandar Rikalo

This patch resolves KDE #416285.