The current configuration of the x86-64 VxWorks runtimes does not support
atomic primitives. x86-64 VxWorks was missed from the previous patch.

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

gcc/ada/

	* libgnat/system-vxworks7-x86_64-kernel.ads: Set
	Support_Atomic_Primitives to false.
	* libgnat/system-vxworks7-x86_64-rtp-smp.ads: Ditto.