ada: Remove No_Dynamic_Priorities from Restricted_Tasking

Some of our restricted runtimes support dynamic priorities. The binder
needs to generate code for a restricted runtime even if the restriction
No_Dynamic_Priorities is not in place.

gcc/ada/

	* libgnat/s-rident.ads: Remove No_Dynamic_Priorities from
	Restricted_Tasking.

• [DBH] gcc/ada/libgnat/s-rident.ads

ada: Support setting task affinity on QNX

QNX does not support setting the thread affinity via a POSIX API.
This implementation uses QNX's native Thread_Ctl API to set the
thread affinity for Ada tasks.

gcc/ada/

	* libgnarl/s-taprop__qnx.adb: Implement Set_Task_Affinity.

• [DBH] gcc/ada/libgnarl/s-taprop__qnx.adb