The Linux futex interface uses relative timeouts anyway, so this avoids
a double round-trip through clock_gettime: once in Qt code to calculate
absolute from relative and once in libc for reversing.
Glibc does not offer such a function because its pthread_cond objects
use a kernel interface that works on absolute times.
Change-Id: I8fbcd3f73d4364a16716b0eea17e8f5f9ab5cd05
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>