* ruby_atomic.h (ATOMIC_CAS): added.

* signal.c (ruby_atomic_compare_and_swap): ATOMIC_CAS implementation
  for non-VC/gcc platform.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@44950 b2dd03c8-39d4-4d8f-98ff-823fe69b080e