[Ada] Expose and use type-generic GCC atomic builtins

[Ada] Expose and use type-generic GCC atomic builtins

gcc/ada/

	* sem_ch12.adb (Analyze_Subprogram_Instantiation): Also propagate an
	interface name on an intrinsic subprogram.  Remove obsolete comment.
	* libgnat/s-atopri.ads (Atomic_Load): New generic intrinsic function
	(Atomic_Load_8): Rewrite into instantiation.
	(Atomic_Load_16): Likewise.
	(Atomic_Load_32): Likewise.
	(Atomic_Load_64): Likewise.
	(Sync_Compare_And_Swap): New generic intrinsic function.
	(Sync_Compare_And_Swap_8): Rewrite into instantiation.
	(Sync_Compare_And_Swap_16): Likewise.
	(Sync_Compare_And_Swap_32): Likewise.
	(Sync_Compare_And_Swap_64): Likewise.
	(Lock_Free_Read): New generic inline function.
	(Lock_Free_Read_8): Rewrite into instantiation.
	(Lock_Free_Read_16): Likewise.
	(Lock_Free_Read_32): Likewise.
	(Lock_Free_Read_64): Likewise.
	(Lock_Free_Try_Write): New generic inline function.
	(Lock_Free_Try_Write_8): Rewrite into instantiation.
	(Lock_Free_Try_Write_16): Likewise.
	(Lock_Free_Try_Write_32): Likewise.
	(Lock_Free_Try_Write_64): Likewise.
	* libgnat/s-atopri.adb (Lock_Free_Read): New function body.
	(Lock_Free_Read_8): Delete.
	(Lock_Free_Read_16): Likewise.
	(Lock_Free_Read_32): Likewise.
	(Lock_Free_Read_64): Likewise.
	(Lock_Free_Try_Write): New function body.
	(Lock_Free_Try_Write_8): Delete.
	(Lock_Free_Try_Write_16): Likewise.
	(Lock_Free_Try_Write_32): Likewise.
	(Lock_Free_Try_Write_64): Likewise.
	* libgnat/s-aoinar.adb (Atomic_Fetch_And_Add): Use type-generic GCC
	atomic builtin and tidy up implementation.
	(Atomic_Fetch_And_Subtract): Likewise.
	* libgnat/s-aomoar.adb (Atomic_Fetch_And_Add): Likewise.
	(Atomic_Fetch_And_Subtract): Likewise.
	* libgnat/s-atopex.adb (Atomic_Exchange): Likewise.
	(Atomic_Compare_And_Exchange): Likewise.