real_time.clock is not monotonic

[frederic.ormancey@atosorigin.com]

I'm porting a GNAT application from Windows to Linux platform, and the
application use two kinds of clock data :
- Ada.Calendar.clock to obtain machine date and time, affect by NTP
and daylight saving
- Ada.real_Time.Clock, which use System.Os_Primitives.Monotonic_Clock
to obtain a monotonic clock (for delays and time events generation)

With Windows version of GNAT (3.15p), all is OK, monotonic clock use
QueryPerformanceCounter() Win32 call to obtain a monotonic behaviour,
but in Linux implementation of Gnat RunTime, Monotonic_Clock is a
single rename of calendar.clock, which use gettimeofday() system
call !!!!

I'll alert Gnat community with this bad implementation, as
gettimeofday() is affected by NTP and others date adjustements. in
LRM, Ada.Real_Time.Clock shall be monotonic => Gnat runtime is not
compliant

This bug was detected with 3.15p Linux version, but implementation is
still the same with latest source of gnat runtime (s-osprim.adb).

Did someone have a solution for this problem ? another implementation
using a Linux monotonic clock ?