compare_and_swap reorganization. This should finally make it compile on MacOS X.

compare_and_swap reorganization. This should finally make it compile on MacOS X.

* src/threads/atomic.hpp: Reorganized namespace declarations.
(CAS_32_functor, CAS_64_functor, CAS_chooser, CAS): Helper templates for letting
the compiler figure out which version of compare_and_swap to use.

* src/threads/atomic.cpp: generic_compare_and_swap now lives in namespace Atomic.
* src/native/vm/sun_misc_Unsafe.cpp: Adapted usage of compare_and_swap.

* src/vm/jit/alpha/md-atomic.hpp: Adapted to new namespace.
* src/vm/jit/arm/md-atomic.hpp: Likewise.
* src/vm/jit/i386/md-atomic.hpp: Likewise.
* src/vm/jit/m68k/md-atomic.hpp: Likewise.
* src/vm/jit/mips/md-atomic.hpp: Likewise.
* src/vm/jit/powerpc/md-atomic.hpp: Likewise.
* src/vm/jit/powerpc64/md-atomic.hpp: Likewise.
* src/vm/jit/s390/md-atomic.hpp: Likewise.
* src/vm/jit/sparc64/md-atomic.hpp: Likewise.
* src/vm/jit/x86_64/md-atomic.hpp: Likewise.