[Ada] Disable Support_Atomic_Primitives on QNX and VxWorks targets
The current configuration of the QNX and VxWorks runtimes does not support
atomic primitives.
gcc/ada/
* libgnat/system-qnx-arm.ads: Set Support_Atomic_Primitives to
false.
* libgnat/system-vxworks7-aarch64.ads: Ditto.
* libgnat/system-vxworks7-aarch64-rtp-smp.ads: Ditto.
* libgnat/system-vxworks7-arm.ads: Ditto.
* libgnat/system-vxworks7-arm-rtp-smp.ads: Ditto.
* libgnat/system-vxworks7-x86-kernel.ads: Ditto.
* libgnat/system-vxworks7-x86-rtp-smp.ads: Ditto.