linux: Add support for clock_getres64 vDSO

No architecture currently defines the vDSO symbol.  On archictures
with 64-bit time_t the HAVE_CLOCK_GETRES_VSYSCALL is renamed to
HAVE_CLOCK_GETRES64_VSYSCALL, it simplifies clock_gettime code.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>