[parrot/parrot] e0289f: fix apple clang --optimize

[GitHub]

  Branch: refs/heads/smoke-me/travis-osx+win
  Home:   https://github.com/parrot/parrot
  Commit: e0289f87d88f06dfba31730ed40ef57ca7715ee6
      https://github.com/parrot/parrot/commit/e0289f87d88f06dfba31730ed40ef57ca7715ee6
  Author: Reini Urban <rurban at cpanel.net>
  Date:   2015-12-13 (Sun, 13 Dec 2015)

  Changed paths:
    M config/auto/cpu/i386/test_gcc_cmpxchg_c.in
    M include/parrot/compiler.h
    M src/atomic/gcc_x86.c

  Log Message:
  -----------
  fix apple clang --optimize

define __WORDSIZE there, which is missing

See https://travis-ci.org/parrot/parrot/jobs/96623113
darwin clang failed the PARROT_HAS_AMD64_GCC_CMPXCHG test