Simplify systemtime_get_time

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Allocate the clock service on OS X once rather than everytime the clock is read

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Fix return type

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Fix framwork linking for Quartz support

Signed-off-by: Mattias Andrée <maandree@operamail.com>