Move Yield_Hook from the implementation unit System.Once to the runtime unit System.Synchronous_Control
Remark
Move not required children of System.Tasking to the outside
Merge commit 'e934551' into gcc-4.7

Conflicts:
	source/tasking/s-tasks.ads (modified)
	source/tasking/s-tassta.adb (modified)

Modifications:
	source/tasking/s-tasks.adb