Now ARM traditional doesn't have weakCompareAndSwap() implementations
in Atomics.h as ARM64, ARM Thumb2, X86 and X86_64 have. After we have these
assemblies, we can set ENABLE_COMPARE_AND_SWAP to 1 in Platform.h too.
( This bug was revealed by https://bugs.webkit.org/show_bug.cgi?id=127678 )
After https://trac.webkit.org/changeset/190103 we don't need assembly CAS anymore.