This patch fixes failures due to the use of 64-bit atomic
operations on ppc-linux. Undo of the previous patch for 64-bit atomic
operations only.

Note: this does NOT address the failure on ppc-darwin, which will be addressed
by another patch soon.

Tested on x86_64-pc-linux-gnu, committed on trunk

2012-07-17  Vincent Pucci  <pucci@adacore.com>

	* s-atopri.adb (Lock_Free_Try_Write_X): Atomic_Compare_Exchange_X
	replaced by Sync_Compare_And_Swap_X.
	(Lock_Free_Try_Write_64): Removed.
	* s-atopri.ads (Sync_Compare_And_Swap_X): Replaces previous
	routine Atomic_Compare_Exchange_X.
	(Lock_Free_Read_64): Renaming of Atomic_Load_64.
	(Lock_Free_Try_Write_64): Renaming of Sync_Compare_And_Swap_64.