[Ada] Make Max_Sensible_Delay uniform across all Posix targets

[Ada] Make Max_Sensible_Delay uniform across all Posix targets

For instance: 6 months where Duration is 64bits.  Heretofore LynxOS was unique
in having an approximately 12 days max delay. By experimentation the actual
maximum was determined and all relevant delay and sleep procedures rewritten to
incrementally wait if necessary.

2018-05-25  Doug Rupp  <rupp@adacore.com>

gcc/ada/

	* libgnarl/s-osinte__aix.ads, libgnarl/s-osinte__android.ads,
	libgnarl/s-osinte__darwin.ads, libgnarl/s-osinte__freebsd.ads,
	libgnarl/s-osinte__hpux.ads, libgnarl/s-osinte__kfreebsd-gnu.ads,
	libgnarl/s-osinte__linux.ads, libgnarl/s-osinte__lynxos178e.ads,
	libgnarl/s-osinte__qnx.ads, libgnarl/s-osinte__rtems.ads
	(Relative_Timed_Wait): Remove.
	* libgnarl/s-tpopmo.adb (Timed_Sleep, Timed_Delay): Rewrite to allow
	for incremental looping. Remove references to Rel_Time and
	Relative_Timed_Wait.
	* libgnat/s-osprim__posix.adb, libgnat/s-osprim__posix2008.adb
	(Timed_Delay): Make separate.
	* libgnat/s-optide.adb: New separate procedure.
	* libgnat/s-osprim.ads (Max_System_Delay): New constant.
	* libgnat/s-osprim__lynxos.ads (Max_Sensible_Delay): Set to 6 months.
	(Max_System_Delay): New constant.

From-SVN: r260724