Abstract IR generation of array cookies into the C++ ABI class and

implement ARM array cookies.  Also fix a few unfortunate bugs:
  - throwing dtors in deletes prevented the allocation from being deleted
  - adding the cookie to the new[] size was not being considered for
    overflow (and, more seriously, was screwing up the earlier checks)
  - deleting an array via a pointer to array of class type was not
    causing any destructors to be run and was passing the unadjusted
    pointer to the deallocator
  - lots of address-space problems, in case anyone wants to support
    free store in a variant address space :)

llvm-svn: 112814