Add a missing || defined(XEN) which cause Xen non-DIAGNOSTIC kernels
to panic at boot.
Provide C++ 2011 <atomic> support functions for hppa and arm.
Revert implicit attribute (module) declaration for options (flag/param).

Flag and param are to change contents of attributes (modules).  These don't
have code (*.[coS]).

Filesystem definition still defines an attribute (module) implicitly.
Use tlb is variants for MULTIPROCESSOR
Revert troublesome ath_hal config definitions back to the original.

This means that, under the new config(1) modular build, if the option
ATHHAL_AR5210, that extends the ath driver to support AR5210, is selected,
the relevant 10 ar5210_*.c files end up being embedded into the "netbsd.ko"
module, which is pretty much opposite of modularity.
Avoid "unhandled relocation of type 3 for" error when load module.
"insmod zbsdmod.o" is successful now.